When I think of unbound forms I think of commercial applications, like those made for data entry. You enter all fields and hit SAVE. If you do not hit SAVE, everything exists only in memory and can be cancelled.
This can be important depending on the business. For example, a notice may be generated, printed, and mailed x minutes or days after saving, to allow time for corrections to be made. Cancel can also help a user "back out" of changes that they made that they no longer want or, "just in case" they bumped anything while looking through a record containing personal or application information.
Since this functionality is so prolific, I'd almost say standard, when using Access, users are confused as to why there is no save button. That is why on my form I include a label that says Autosave: ON so they know what is going on.
I think for the most part the pros of autosave in Access outweigh the cons and most of these things can be dealt with via smart design and user training. Just some food for thought.