Wanted to write this for a year but never got around to it. While riding your carno, you are still prone to getting knocked off it by a wild Raptors pounce attack. Not sure how it's possible, but I found out the hard way.
Tamed carnos are excellent almost all around: their health, attack speed, and base damage allow you to take on most of the creatures on the island, including Rexes and Alpha Raptors. Having a mated pair greatly strengthens this quality. They run fairly fast and can carry a lot, making great transport mounts. They are a fairly good harvester of meat and prime meat.
Their only real disadvantage is a slow stamina regen, even when stood completely still.
Very useful mid-late game, I have a carno lvl 218 with 4 raptors lvl 180+ and they can escort me anywhere. They kill Rex's like is no big deal. The only thing we can't defeat are titans. The day will come......