My reason was the random battery drain which was usually accompanied by the start screen hanging or "resuming" for a minute. I'm leery of trying 8.1 again until the OTA but today I saw a bunch of people saying unpinning Cortana's tile fixed the battery drain. Anyone with battery issues try that?
I have done this and so far so good though I wasn't using Cortana at all just had it pinned so weird glitch if that was the issue.
Before that mine would lock up when I unlocked the phone or it would hang and overheat and drain battery quite often and that was after doing a hard reset (I was just testing to see if the hard reset fixed any other minor issues I was having after the DP upgrade / I didn't do a restore installed all apps fresh on the hard reset) but it caused an unusable phone for the most part.
Other things that I did at the same time:
1. Removed / Rebooted and tested without the extras and info. No more lockups or overheating. After a bit reloaded extras and info and still had no issues.
2. Removed Perfect Battery. (I don't even see this in the store anymore on a search)
3. Installed Flashlight which gave me the battery number on the lock screen and home screen that I wanted from Perfect Battery plus a handy flashlight.
So now I am even using the built in battery saver which I never could use before because of the ongoing issues I was having.