One extremely minor and subtle point (that you could safely ignore and probably never have it matter, ever):
If you play a Tactician but have nothing to discard, you know right away that it will have no effect after the current turn, so you discard it during cleanup the turn it is played. If you play an Outpost when you're already taking your 2nd turn in a row (either because of Outpost itself, or because of Possession), it doesn't "know" it won't give you another turn after this one until it actually tries to do that (and fizzles), so you don't clean it up this turn.