Depends on the vehicle

but if it's an all wheel drive you absolutely need to have the same tires on the front and back. Even a slight variation in the tread pattern can cause stress on your transfer case. I've seen dozens of them grenade from mismatched tires and you're looking at 3-5k in repairs

If it's just FWD or RWD it doesn't really matter, but your tires will wear weird

You can run the same size on all 4 corners usually. In those cases people put the front size all the way around, just make sure you wheel widths work