I ran bikes on my roofs of two vehicles for years with Yakima mounts.
While it was pretty easy to lift them up there, I almost hit the bikes once following a friend through a drive-thru on our way up to go mountain biking at a ski resort one summer.
I did not think anything about it until I was already in line.
Luckily there was room by just inches for me to go through.
The hitch rack on my FJ earlier in this thread is so much easier to load/unload the bike now.
Plus I think it is more protected from road debris this way too.
With them up on the roof they are subject to anything flying through the air.
Long ago my black Raleigh above took out a bird in Spokane.
What a mess.
With them on the back of the rig (my first hitch mount), they are somewhat protected by any debris from the rear door shielding them.