When I click save or hit Command + S what appears to be a new version of the document is created. So if I save 2 times, I get 2 documents, filename.blend1 and filename.blend2.
What exactly are these files and why is Blender creating them?
When I click save or hit Command + S what appears to be a new version of the document is created. So if I save 2 times, I get 2 documents, filename.blend1 and filename.blend2.
What exactly are these files and why is Blender creating them?
These are backup files created by Blender and are fairly normal.
Excerpt from the wiki
Save and Auto Save
...To reduce the chance of losing files when those events occur, Blender can use an Autosave function. The File tab of the User Preferences window allows you to configure the two ways that Blender provides for you to regress to a previous version of your work...
The other two answers have covered this already, but I just thought I would go further and show you the preference concerning this feature.
If you go to File→Preferences→File, you will have a box that says "Save versions #" (Where # is the number of versions to save).

If you want it disabled (if for example, you use a cloud service for backups), set it to "0".
These are backup files, saved and incremented every time you make a save. Unless you really know what you are doing and aren't creating giant files I would leave this setting as it is. One day you will want to retrieve critical blend information after an unexpected crash by loading one of those backups, and wish you hadn't disabled it. This can be an extra 'fail safe' in the unlikely event that 'recover last session' doesn't work.
These days storing data is so cheap, the only problem you might face is the organization of so many files. These files are fine to delete after a while if you really don't need them, or won't be working on a .blend anymore.
/tmp on a timed basis. See the wiki
– gandalf3
Dec 02 '13 at 09:07