If you are running out of free space on your startup disk and you suspect Deja Vu, check your Safety Net Archives folder (found in your Documents folder by default). If the archives there are taking up too much space, consider doing one of the following:
1. Disable Safety Net in Deja Vu's Options.
2. Tell Safety Net to keep fewer archives.
3. Choose a new location for the Safety Net folder (i.e., on a different disk).
Assuming that you are backing up to a different volume (which you should be), Deja Vu does not create files of any significant size on your startup disk apart from Safety Net archives (if you have it enabled, and have not changed its default location from Home/Documents).