Pretty big complaint in some games, but it's great in others. A game that does it well is like PowerStar Golf, where if you get an incredible shot in, the game auto-records and uploads that moment. It's usually shorter than a "Record That" recording. Of the dozens of hours I've played, it's only done it maybe 5 times and in every case it's for something that's pretty great, eg., a hole in one or a long chip shot, etc.
An example where it's really bad is in Madden '15 and FIfa '15, though I think EA tuned it down for both with a recent update... But in Madden '15, it auto-records every touchdown and posts it to your profile, even if you didn't score them. So, if the CPU does a 2-yard touchdown run, it records it as a "MAdden moment" and uploads it. Same with Fifa, if your goalie makes a block or the opposing team scores, it publishes it.
you can turn it off, but the only way to turn it off is at the OS level and it turns off *all* recording from Game DVR, which sucks because I still want the ability to record, I just don't want titles auto-recording and publishing for me.
It wouldn't be a problem at all if it wasn't abused by some developers/publishers.