Here's my opinion.
1) A lot of us have nothing left to do, so why not horde engrams and edge factions?
2) It's not more enjoyable to make progress in the moment and let me tell you why. I played so much PvP year 2, 100s of hours and I've not gotten a single God rolled longbow/Luna/1000 yard stare. Im also short on 5-5-2 build, meaning I need more 96+% rolled gear that fits my wants (HC reload, int/disc with nade throw). By doing things to help get those since the odds are already tiny to get your near exact wants.
2.1) sidenote: not everyone is using it to get to max level right off the bat, it's more of a headstart.
3) Saving engrams takes 0 effort. The only part that takes effort (for some) is figuring out what to delete from inventory/vault to make room.
It makes the game more fun to have a headstart and obtaining packages off the bat, imo.
Also, we want to be as raid ready as possible for Friday and this helps.
Of course there probably are some people that will spend 1 to 2 hours in getting as high as they can before starting anything and to them it's probably fun. It doesn't really take out any excitement from the new stuff, regardless.