The problem I've always had is making it habit. I've created different play lists and added videos to them and watch later, but forget about them and then notice weeks later I have stuff in my watch later list I never watched.

Put another way, I find adding to watch later easy, but I find remembering there's stuff there to watch very hard. I'm sure YouTube could make this much easier, but I doubt they view intentional watching as better than stumbling through random stuff for hours.