No - not really. I do just because the top side tends to look prettier - so if I'm cooking something to make it pretty - I'll flip it so both sides look nice. If not - I don't bother flipping. This holds true for marinated meat. If you're cooking meat with breading or seasoning - you definitely want to flip so both sides get even hot air flow. Otherwise your bottom side of the breaded meat will be soggy instead of crunchy!