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......
Carnos are excellent mounts and hunting and battle companions. At mid-level, my pack of five have speed slightly superior to a raptor and strength comparable to a low level Rex. Focus on building melee, speed and stamina. Combine them with a couple raptors, a Rex and a Trike and there will be very little you can't overcome.
I tamed a level 30 carno everything went fine until a level 30 wild Rex came in my base my carno took it on and won saving my butt. Leveling up melee damage and health as well as stamina to do this. Note: My carno had 175 melee and 1300 health.