If you use a rototiller do it only to make the first break into tough soil or to turn under amendments lightly, like "folding" in ingredients into a batter. Don't go over and over a bed to make it smooth or you can ruin the soil's tilth.
It's especially bad to till soil that has enough clay in it to feel sticky or slippery. The rotating tines of an 8hp tiller beat DOWN on the soil below their rotation with (surprise!) eight horse power. That can pack the subsoil so hard that water backs up into the bed, ruining drainage by creating a perched water table.