I rarely enslave anywhere, it's just not worth the hassle of all the additional population in your governed settlements. Better one problem settlement that takes a while to settle down than lots of trouble at home. I always occupy and install type IV (though not in Ariminium, that goes straight to type I).

I will, however make an exception on the no enslaving rule in Greece when I eventually conquer that. Same for when Carthage is finished off too.