There are a couple of things which might be happening to your files. The first would be the result of "shadowing", the term for the way in which Microsoft archives its files. When you save a file it could easily double in size OR SOMETIMES even be cut to half its size. This is not a predictable change; you can change your file just by repeated saves.
A file will stay between the high and low file size as it is archived (even if nothing else is changing in the file.
See the Microsoft Knowledge Base for further information.
Another explanation, but doesnt seem to be relevant to your case, which would account for a large change in file size, has to do with configurations. When a user uses many configurations in a session, SolidWorks may store multiple configuration bodies in the part file to increase performance when the file is used the next time it is brought up.
Shadowing is inherent in the way that Microsoft provides a "transacted access" (and I'm still not sure what that term means yet) to the file. For example: When saving a document, the new data does not become available until the change is committed. This ensures that the file is always consistent; it helps with error recovery and ensures that data is not lost or trampled from the existing good file. In addition, it helps avoid data corruption in the event of the software terminating unexpectedly, since the file has not been fully "committed." Shadowing also helps eliminate arising from "out of disc space" (again the file has not been fully committed). Finally, its helps prevent file corruption problems caused by network file server crashes while saving.
There are other ways to guard against this, such as a temp file method of file storage (This is not to be the same as SolidWorks autobackup/autorecover).
Shadowing offers these advantages over temp file commitment.
Temporary files may not be able to be created, due to folder permissions (shadowing only requires write access to the file). Remember temp files get opened in the same directory as the source component.. and imagine opening a part from a read-only folder..
Temporary files can't be used to replace the original file if it is opened (read-only) by other users, regardless of whether the read-only file was opened before or after the full write permission copy is used.
Temporary files can sometimes be unstable when a file is saved with one name, then resaved with a separate file name, especially when disk space is low, or the OS is temporarily unstable.
Regards,
Jon
jgbena@yahoo.com