That has to do with what your users are putting into the database. If you change the upload size to 10 MB, that means that users can upload files with a size of up to 10MB. So any single file can be 10MB or smaller. When you change it to something else, you are setting the maximum file size for any particular file uploaded to the Document Library.
Because you are storing these files in your database, effectively, they become BLOBs in your database. So you may want to review your database capacity before deciding to change this setting just to make sure that you won't run out of space in your database for the foreseeable future (and that any backup procedures you have for your database are adequate to store the amount of data you will need to store).
The only other "ill effect" that I can think of is the performance penalty for storing binary files in a database. You generally can get better performance by storing files on the file system. If, however, it is currently performing well enough for your needs, this may not be an issue.
Hope this helps!
--Rich
