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.
Having a pack of Dilos is a good way to combat one early on: they can slow it down with their spit attack, they can be generally hard for it to consistently hit, and carnos focus more on dinos than humans so if you get ambushed chances are it might change focus to your dilos. It can be possible to kill a carno with just 2 dilos if they can take a hit and you provide cover fire with any ranged option.
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......