I've wondered about how restoring a backup impacts things, in conjunction with a factory reset.
To use a PC analogy, say my computer is running poorly. I back it all up (Windows, my programs, files, etc), and format the drive. But then, instead of reinstalling Windows from scratch, I simply restore my backup, putting everything back the way it was. The odds are pretty good that I will still be having the same poor-running problem. Formatting then reinstalling Windows and my programs, then copying my data on again, is likely more effective at making it run well again.
My Verizon G4 had heat and battery life problems. I did a factory reset on the 2nd day I owned it, then used Tap and Go to transfer my apps, etc, again from my S3. I only used it for a day before doing the factory reset, so I can't say if it improved/changed after the reset.
The reset didn't fix my issues for me. But perhaps I shouldn't have used Tap and Go while setting it up again, maybe I should have manually installed my apps, etc. However, that would have taken a long time, so it wasn't very appealing.