I only don't bother with one if I'm brewing something like a wheat beer with <15g of hops in the boil. Otherwise at the end of the boil it doesnt form a nice neat cone like hot trub does so you end up wasting too much wort. If you pour it all into your fermenter anyway, with IPA's the hop sludge can end up higher than the tap, which blocks it, and then you're stuffed.