I don't see anything wrong with thinning out your hair, if that's what you want to do. I'm very much against it for myself, but I don't know how it would hurt your hair. Others may know more about this. Such as are scissors or razors better. (I would guess scissors might be better for your hair?) However, as far as the poofiness goes, thinning can add to the poofy since when those thinned out hairs grow back they could seem poofy/frizzy, whereas if you keep it long (and this takes time) the length will pull the poof down.