Why would you want to reverse pick-pocket anyone?
A variety of reasons already mentioned - you want those NPCs to live, you like them, you're feeling generous, you've got 800 suits of Talon armor in the locker at your house, you're bored.
And one other reason that people haven't mentioned here is.... on PC, with fancy clothing mods, it's nice to dress up the population in some of those clothes.

(Oh, and the hostile version - reverse pickpocketing live grenades and mines to blow folks up. Never tried that, but FO3 kept a statistic for it. Heh.)