Well yes, that is a good quality and is one of the reasons I think manual saves and in-level autosaves make a great team and I also think they 'should' in fact co-exist, but there is no reason to pick only one of the other, it is just limiting the player's freedom over his/her play style. I for example like backtracking even in linear games and I love exploration but without manual saves this becomes rather risky because if you want to save after having spent a while exploring you need to pray that you won't get yourself killed before the next checkpoint is reached.