Well no it won't impact you as a player but, unless you put all the Pokemon you want to keep in Poké Bank, you'll lose everything. It's also just easier to have the Legendaries given to you rather then restarting the whole game just to get better ones.
It's really a sense of "I like being able to control what I get/have" and also having multiples of everything for multiple sets. At least without resorting to illegitimate methods, which I don't feel right using.
But my biggest issue is that if I reset, I lose the Oval Charm of all things, which means if I reset both games, I need to complete at least one regional pokedex before I can resume breeding pokes as I normally would.
...probably a weird concern to have thinking on it, especially concerning all the money, items, berries, clothes, decorations, etc etc etc that have more value...
and yes I have banked everyone I wish to keep, including the likes of the pokes I use in battles, event pokes, a few pokes I was still breeding in my original games, and even trade fodder legendaries (because people really like to soak those up in the GTS for some reason...)