like everything else in poker it depends on the game you are in. With alot of loose calling of preflop raises you don't always want to raise 8bb because you might get called in 3 or 4 places and then get a crummy flop for your aces. In this type of game pushing is an option because you will get called most of the time which is good for you. In a passive game limp from early position hoping someone wakes up with kings or queens and you can get all in with a reraise maybe. In late position or the blinds raise twice what is in the pot, and you might get one caller. Your table image is really important too.