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.

Doesn't get stuck as easily as the larger carnivores

Carnos can be used for cave expeditions, especially central cave where they can right click attack everything. Just get out before night!

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......