I'm trying to keep my levels even across my entire party in this playthrough, and I'm avoiding prepromotes as I do in past FE games (I've beaten 7, part of 8, 9, and 13), but it's kind of wearing me down. I'm on Birthright, and I'm pretty sure I would be crushing it if I didn't want to spread my EXP around to everybody, and focused on a core group of ~12-16 units.
But my inner completionist wants all the children, which means that it's in my best interest to use everyone so that they all support points. It's making things take way longer than they need to, and I'd probably wait at least a year before I get around to Conquest.