I am glad I brought up this topic, since we are seeing divergent answers and some new questions being raised. I think I have other follow up questions as well now, but have to be at my DAW which is at home....later

In theory, either method should work.  But I've found that when attempting a quick cut/boost of the level, say to reduce a harsh sibilant, the volume envelope sometimes won't make the cut at the right place -- if I manually draw the cut right where I want it, the envelope won't necessarily cut it there, but at some nearby spot instead.  So for those, I just split the offending sound into its own clip and use the clip gain to reduce its level.  Seems to work better.
 
Cheers,
Eddie
 

POST FADER
VERSUS 
 
PREFADER
 
 
PLUS
 
EFFECTS IN LINE (NOT NECESSARILY 'SEND AND RETURN')
 
IF YOU INCREASE GAIN WITH AN ENVELOPE,
YOU WILL DRIVE YOUR EFFECTS HARDER AT THE SAME TIME.
 
which can cause clipping and/or distortion/harsh sound
 
gain structuring is key to clear sound.
 
 
no effects, no anything but the clip, then it simply raises the gain of the clip for that automation period.

batsbrew
POST FADER
VERSUS 
 
PREFADER
 
 
PLUS
 
EFFECTS IN LINE (NOT NECESSARILY 'SEND AND RETURN')
 
IF YOU INCREASE GAIN WITH AN ENVELOPE,
YOU WILL DRIVE YOUR EFFECTS HARDER AT THE SAME TIME.
 
which can cause clipping and/or distortion/harsh sound
 
gain structuring is key to clear sound.
 
 
no effects, no anything but the clip, then it simply raises the gain of the clip for that automation period.

 
Nailed IT!!!!

Thanks for that … Sonar help tends to be confusing as seen in the following:
 
I found this in Sonar's help under "Creating and Editing Audio Envelopes":
 
“Note: When you add a “gain” envelope to a track in SONAR, you increase the track’s level post-effects, or after the effects processors. Some hardware mixers call this level “volume,” because it is post-effects, but other mixers refer to this as “gain.” Either way, SONAR’s gain envelopes increase a track’s level after the effects processors in the signal chain.”
 
I found this in Sonar's help under "Drawing Envelopes on Clips":
 
“Note: The Trim value of a track is actually a clip parameter, not a track parameter. SONAR applies clip volume settings, including Trim, to a clip before the clip’s audio data reaches any plug-in effects. Effects can sound very different when their incoming data changes volume, even if the final volume is unchanged.”

This link is your friend:
SONAR X2 Signal Flow Diagram
 
Most important:
 
Clip Gain > Track FX (gate? compressor?) > Track Gain
 
Realising that fact made an incredible difference to my ability to sculpt the sound the way I wanted it. Strange things would happen before I figured that out, because every time I adjusted the clip gain, my gates and compressors affected the signal differently.

Stickman could you elaborate a little on what you are saying --about how you use (or don't use) clip gain / versus track volume envelopes..... thanks !!! 

OK. I had a bass guitar track, with some variation in recording level and 'noise between the notes'. I set up gate and compressor effects to tame the signal - remove the worst of the noise and level out the volume.
All was fine and good until I decided to use a clip gain envelope to boost the level of the bass in the first verse.
What happened - and I didn't notice this immediately - was that a) the bass got noisey-er and b) the volume of the bass track didn't really go up as much as I thought.
Of course, now we know why: I was driving the gate with a louder signal, letting more noise through the gate, and the compressor was doing its level best (sorry!) to prevent the volume from getting louder.
 
I think this bad practice stems historically from my equating "clip gain" to "track trim" as it used to be called in earlier versions of Sonar. Most people I'm sure never got into the habits I did.
 
I now use track volume envelopes a lot more than I used to. In hindsight, it seems very obvious, but at the time, I thought I knew what I was doing. 
 
Does that explain what I meant earlier?

Yes very much so --- thanks ..

Cakewalk's first mistake was renaming "Trim" to "Gain". That's bound to confuse users of hardware mixers, even if SONAR"s control isn't strictly speaking a trim, which implies a reduction in signal level rather than an up or down adjustment.

If you think of the Gain control as a Trim control it all makes more sense.

I like to start work on a vocal track with a trim/gain envelope. I manually insert nodes in front of each clip and use them to balance their levels. Then I look for sibilance and insert dips for them. This all before adding any effects to the fx bin. That way, when I subsequently add a compressor each clip is hitting the detector at the same approximate level. The result is a smoother, more level vocal track even with gentle ratios.