I'm looking for some advice on ways to free up some space and get rid of some unnecessary files from a few years of sonar and its various versions. Where do all of the overwritten saves go? Where's all the junk stored that is created in the recording process?

If you are using per-project audio folders, all the unused takes and tracks are stored in the project audio folders. If you are not using per-project audio folders, everything is in the global folders. There are two ways to clean them up, bundle the projects or with per-project audio folders enabled use the "Save As" function with "Copy all audio with project" enabled in the Save As dialog. Once you have validated the newly created projects, the old projects can be safely deleted.

Do you think it would free up a decent amount of space?

just a tip if you want to free up some space quickly.
 
open windows explorer and click on your C Drive.  do a search for *.pdf.  this will do a search on your main C drive for every pdf file in all directories.
 
at the bottom you should see the results and it will say something like 129 files found click on the details.  highlight all the found PDF files and it will tell you how much all these PDF files are taking on your C Drive.
 
I found 129 files and it was 498MB on my main C Drive.
 
I right click and cut them and paste them to a removable USB Drive in a folder called manuals.  I can quickly find any pdf manual I need and they aren't on my main drive anymore.
 
just a really quick way to move off some files and free some space that you may really need.

keneds
Do you think it would free up a decent amount of space?

It could especially if you have a lot of unused takes or deleted tracks in your projects. Deleting a version of SONAR frees up less than 200MB.

I wouldn't delete all the pdf files on my PC or copy them to a flash drive.  Most (all that I know of) are ones that I want to keep.  Many of them are user manuals on hardware or software I have. 
 
I have 70 pdf files (they are kept in a separate folder) and they only total 305 MB.  That's relatively nothing with the size of modern hard drives.
 
 

Boy I stopped worrying about hard drive usage back when we moved from 80 Gig drives to 250 Gig drives. Now with 1 and 2 TB drives I don't think one of my drives has ever exceeded 30%. 
But I do like to keep things tidy myself so older projects are stashed away on my 3rd DATA drive. I only keep up to date albums I'm working on in my main Sonar folder. 
I don't no how old or how small your drive is, but your living dangerously if you don't have it backed up. Twice or 3x. 
Myself if faced with your situation I would not delete anything until you back it up. And back it up as is , don't worry about the deleted tracks, deleting stuff is dangerous. . I'd just archive them to a DATA drive, an external drive or DVD's if your so inclined. 
 
Once you've done that I would use the " Save As" "Copy audio with folder"  option mentioned above and put everything in a fresh folder. 
Open them if possible to double check they play and load. 
Now it would be safe to delete the original files. 
 
I don't use my main OS drives for more than 2 or 3 years. I update them and move them to be used as DATA drives, Then they are retired to the shoe box after  around 5 years. 
Treat yourself to a  nice fresh OS drive.. a SSD if you can. 
For a desktop DATA drives the best bang for you buck is a 7200 RPM SATA  1 or 2 TB drive for about $55- $80  these days.
If you have a laptop then a 1 TB external drives are around $65-$100 depending on sales. 
 

I have a 300 Gb drive. I have about 100 Gb of space left. I have around 20 projects plus various plug ins. I back up my cakewalk projects file on occasion. I was just wondering....where do all of the deleted takes, tracks and multiple overwritten saves go?

keneds
 I was just wondering....where do all of the deleted takes, tracks and multiple overwritten saves go?

Any Audio files that were only connected to a deleted track are in the audio folder.
Audio files that were replaced in a track with a clip bounce are in the audio folder.
Some history of deleted tracks/waves,.... is in the project file.
Sonar's Overwritten files are gone.
Anything you deleted on the audio disk is in the recycle bin, on the audio disk.
 
As described: to clean a project of no longer needed audio files, open the project, SAVE AS to new name in a new folder, check the box to copy audio.
If you have been using project audio folders you can use a windows explorer to compare the audio folders.
If not, I suggest you open each project and save as to new folder with project audio folders.
When completed you can delete all the wav files from the default audio folder.
 
Also: depending upon the settings for the OS (system restore, volume shadow service, file history service), some shadow copies, and file copies, and undo stuff, may be stored in hidden folders.
 
I have system restore ON for the OS disk and OFF for the audio disks. File history wants to copy doc files to a 2nd disk. I have this off.
 
Regularly: perform disk scans to assure the file system is happy for ALL disks, then use disk cleanup for each disk and choose to clean system files: when the 2nd scan is complete, choose the MORE OPTIONS tab and choose to Clean Up System restore and shadow copies. This will delete all but the most recent restore point.
 
The Windows update cleanup can take many minutes and even seem to be hung. I have seen this take 30 minutes on some systems. So be patient.
 
I also delete all the system dump files if the event list is not showing way stupid stuff.
 
While writing this post disk cleanup deleted about 5 GB of stuff on the OS disk.
 
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My equipment:
A small room containing:
chair (semi-comfortable)
steel and fiberboard table:  generic putty colored keyboard, mouse, mixer, controllers
Home-made wooden shelving:  monitors, turntable, tape baker, mics, cassette deck, DVD deck, notes, pencils and pens
Rack:  patch panels, computer, audio interface, midi interface, noise gates, AC power conditioner, Ethernet hub, shelf for notes and stuff
Drawers:  manuals, disks, adaptors, meters, pedals, effects, mics, headphones, and other stuff
Wall shelves:  tapes, manuals, parts, boxes, cables, general storage
Other:  keyboards, guitars, percussion things, amps, tape decks, outboard boxes, and other stuff