I let my PC's spend their own money to train NPCs using Ultimate Campaign Downtime if they so desire (to a maximum level of Character Level -2, so they can 'build' their own potential cohorts, or make some of the local folks. But not all of the NPCs can/should be cohorts, so sometimes the leveling of NPCs is just a way to get access to higher level spellcasting, or to boost a town's defenses. (They gave some training to Sheriff Hemlock and Mayor Deverin in Sandpoint)
Sometimes it doesn't benefit them though. Training Justice Ironbriar kind of bit them in the ass.
I haven't run in to any problems, but what do you think about it?
Very Respectfully,
--Bacon
I like it. Not only does it encourage role playing in a positive way, but it also gives the players something to drop gp on other than a shinier sword to max out DPR.
Thanks, Master Marshmallow,
Our party bard took a shine to a bartender's daughter in Sanpoint (Kidala Viskalai), and ended up training her up from a 1st level commoner to a Fighter(Brawler) 3/Rogue(Thug)2. He also bought a ship.
I really enjoy his character. :D
Very Respectfully,
--Bacon