He's talking about the pure "go here get that" quests. The Brotherhood of Steel side quests for example or the settlement relief ones in Fallout 4. They're put in so you can never technically complete the game but IMO it means sacrificing a lot of genuinely interesting storytelling to be able to state that their game can go on forever. It helps that Fallout's world can be fun as hell to run around in but there's a reason why I haven't played it in months. It gets dull, repetitive and meaningless to play.