Mental health ++
Upsides of multiple system stuff is that while one of you might be having a complete nervous breakdown, the other's in the back going 'Hey. Hey, we know you're tough, you don't have to prove anything, TAP OUT you stubborn bastard!"
And then you go from a depressed wreck to cracking open a cold one with the boys because it's I Don't Give a Fuck o'clock.
And then feel guilty because the rest of your friends can't pit their mental illnesses against each other like you can.