Why route to Master Bus vs. "Speakers"?

I'm sure you will get multiple reasons but here's one: If the audio is clipping, it is safer to have it clip going to your master bus than to clip going straight to your speakers.

Along with the above, that's the last gain staging area, where things can be changed, without disturbing the relationship between the tracks.  I guess kinda what John said.

Control is the key word. 
 
I like to have a Master buss and a few sub buses too. I will most likely have one or two aux buses as well. The sub buses are for routing like instruments together to the same buss. Drums all go to the drum buss and it goes to the master buss. This arrangement lets me have total control over level and FX for all my tracks without having to repeat the same FX and settings on similar tracks. So all the guitars go to a guitar buss. All voices go to a Voice buss and so one. All of those buses will all out to the master buss. Nothing goes to the master directly as a track.
 
With this setup you have control and versatility. I think most of us look at outing directly to the main outs as bad form. Something to avoid. Sonar makes it easy to add buses as needed. Therefor use as many as you need.   

If you don't have a master bus then you have no way of knowing whether the sum of your tracks is clipping. If you just have them routed directly to your interface then you could easily have a situation whereby all of the individual track meters look fine, but the sum is clipping significantly. When you have that master bus meter you have a very clear indication of when the sum is clipping so that you can set your track faders accordingly.

All I know is that when I first started using DAW's (with Pro Tools), my music was distorting really badly and I didn't know why because all of the tracks looked fine, and it wasn't until someone told me to insert a master bus that everything was hunky-dory!

Well the main outs also show clipping. 

The way I export a mixdown is I use the master buss only as the source.  What is on the master buss is the entire mix. The level is what is shown on that buss. 
 
There may be a misunderstanding. The Main outs, also known as the audio device are shown in the Console View. You have meters and two fader for each stereo out. If you have configured your CV right it should have three panes. One for tracks, one for buses and one for the main outs.  

Federal Laws on loudness?

vegas 13 has loudness meters with the legal stuff built in. i now bring my sonar mixes into vegas just to do a reality check - if it's green i'm good to go, red, i gotta bring it down. i can also see if it's too low.

so you can apply effects to the whole mix before it hits the "master" out (speakers)

Karyn

lawp
so you can apply effects to the whole mix before it hits the "master" out (speakers)

The Master out is not the speakers..   You could have (and I do have) more than one set of speakers.
 

sure, i was using the op's terminology, i also have multiple outs

grumbleweed4162
Here's a "good" reason to bypass the Master output:
 
Say you import a reference track (fully mastered) and wanted to compare the sum of your new tracks (that should be going through the Master Buss) and the reference track. 

Yup. This is also the reason you DO want a Master bus, so you can isolate both ways.
 
I use a submaster bus which has all my mix goo on it (console sat, tape sat, widener, limiter, etc.). If I do any stem mixing (which is rare but happens) I can then bypass the submaster and route those to the master. The only thing I put on the master bus is SPAN for referencing. Also, if you have another finished track and wanted to use that as a reference for mixing a transition into or out of for an album project it's another good reason for a master bus (or like said above, a reason to have certain material bypass it)
 

I Use a MAIN OUT  BUS  and a MASTER MIX bus :
 
The MAIN OUT  BUS is the FIRST bus: easy to get to to adjust.
The MAIN OUT bus controls the monitoring volume sent to the audio device, via sonar's main outs.
The MAIN OUT bus does NOT have "effects." And no envelopes.
The MAIN OUT bus has monitoring tools: Voxengo Span, vintage meter, Panipulator (required),...
 
The second bus is the MASTER MIX bus.
   All other Buses output to the MASTER MIX bus.
   Guitars to Guitars All, and then to Instruments All then to MASTER MIX
   All Drum/Purc buses to Drums All,  and then to Instruments All then to MASTER MIX
   Vocals Main, and background, to Vocals ALL then to MASTER MIX
 
The MASTER MIX bus is output to the MAIN OUT BUS.
 
The MASTER MIX bus is used for bounces. All final effects are in the bin.
The MASTER MIX bus may have envelopes for fades and misc. adjustments.
 
I add at least two blank tracks labeled MIX1 and MIX2, to projects.
   These output to the MAIN OUT bus.
   NOT directly to the sound device.
   Not to the MASTER MIX bus.
I solo the mix track to listen to the mix(s).  When listening to the MIX tracks there is no need to bypass the effects/eq, or change the volume setting, of the MASTER MIX bus when listening to a mix track.
 
And because the MAIN OUT BUS volume is the same, I can compare, audibly and visually, the mix with original tracks.
 
Per CJ's insight, if the mix does not sound correct, before I do anything else, I use control-z (undo) to remove the mix clip, and the wav file from the disk. This means I have fewer orphaned audio files.
 
ALSO: I change the name of the mix tracks (add the date) before bouncing-to-tracks so the wav file will have a reasonable name.
 
I never look at, or change, Sonar's Main Audio Outs.
 

No, I want to be better!

John
No, I want to be better!

Think it and you are.

Grundberg
Wow, this became a hot topic! Thank you for the variety of responses.
 
I've been using Cakewalk software for almost a year and I guess it was finally a few days ago I realized why I need a Master Bus. Based on 90% of these responses, a Master Bus is crucial to monitor and control the audio output of my projects.
 
I have ensured that my custom template contains a Master Bus, as this will be an important element in every new project. If I hadn't addressed this to the Forum, I probably wouldn't have thought of doing it myself.
 
As of the past few days, I've been going through all my projects in progress and routing the tracks to the Master Bus as needed. I haven't put much consideration on additional Buses because my skill/experience level doesn't quite call for that requirement yet. (Frankly, I find the use of extra Buses quite complex and intimidating.)
 
I guess I learn something new all the time! Thanks for all of your input on this.

Actually using "stem" busses can make mixing a lot easier/less confusing. Like sending all your drum tracks to a drum bus, all your guitar tracks to a guitar buss (I use one for lead and another for rhythm), a buss for vocals, etc... That way you can get things balanced with the track faders (like your drum kit mixed) then adjust the entirety of each element instead of linking track faders or readjusting things one at a time.
 
Also it's a good place to add overall effects to grouped instruments (again like drums). You can add some full kit compression or reverb or whatever on the bus and control it there instead of having a million instances of the same effects all over the place (which also consumes more computer resources). Then as you get into more advanced mixing you'll be familiar with busses, how they work and how to route them so creating dedicated reverb, compression busses or multi stage stage processing concepts aren't as intimidating.
 
But generally at least having a drum bus, a bass bus, a guitar buss and a vocal bus all outputting to the master is super useful and in a lot of ways LESS complicated/confusing than only using the track strips.