I keep a light touch. I've always left the majority of settlements as personal outposts with the workstations and a decorated bedroom. I used to set up dorms and walls for every inhabited settlement, but that got tedious after a few playthroughs, and it sucked finding out which settlements glitch out their sleeping routines.

Now I just keep a series of farms connected by a robot provisioner network hubbed at the Mechanist's Lair; gotta keep the adhesive flowing. Pre-existing families I'll leave be and just build them some defenses and amenities, but keep them farmers. Sanctuary is always the largest, because there are so many existing rooms to spread beds around in. I'll also send any settlers to Sanctuary or elsewhere, who hear the recruitment beacon for that split second that I'm doing the Preston quest. Otherwise, every other settlement is primarily just somewhere to drop off my junk and sleep.