I... don't. I don't catch enough Pokemon to fill even one box, let alone 10-15 or anything else. Filling the PokeDex has never been a goal of mine, and neither have RNGing/shiny hunting, so I only capture the Pokemon that I'm going to use on my team. And those that are given to me by NPCs, but there aren't that many of those. If I'm using anything other than 'Box 1', then that's very, very unusual for me.