So if there's room in your car it's clear you don't HAVE to have a rack. Though with a muddy MTB or dualsport it'd be nice to not muck up the interior of your car. It comes in handy is if you're travelling somewhere with your bike, or if you and a couple buddies are going somewhere to ride an event or something. I went with a hitch rack as I already had a hitch and there will be times I need the interior cargo space.

Roof racks scare me though, reminded of the insurance commercial at 0:50 https://www.youtube.com/watch?v=zfyWct2FJBU

Guess there's a reason to get a hangtag like this though: