Whereas the Jackass .5 films tended to offer good quality extra footage which could have easily been in the proper movies, 'Bad Grandpa .5' is a DVD special feature disguised as a film. You can see why most of the scenes in this were left out of the movie because they were lacking funny reactions or strong comedic execution from Knoxville. In a way though, this is the point of the film in explaining why certain sketches were left out and showing the issues/processes which are inherent with shooting real life prank-comedy. And to be fair, the parts at the end involving the Irving Zisman (Johnny Knoxville) and Gloria (Spike Jonze) characters together work very well and perhaps should have been in 'Bad Grandpa'.
As I said, This is certainly more of an extended special feature, but saying that, it is worth watching just like any dvd/blu ray special feature if you're interested.