Even when you're mulching you're still throwing grass to the right side of the mower. Mowing counter-clockwise means you're "throwing" towards the part of the lawn that has already been cut so you get better air flow any blow-out can get out without being hindered by tall grass around it. Mowing clockwise when bagging just allows you to get all. You can grab anything that was missed in your overlap the next time around. Personally I mow around the edges 2 or 3 laps clockwise and then go straight back and forth no matter what kind of mower I'm using or whether I'm discharging, mulching or bagging.