WHEN TAMED! On a pvp server mostly make sure 100% of the time he/she is in a separate cage completely away from all other Dino's!! This is because after a certain amount of dmg done to the giga he will begin to "rage" he will turn on you even after all the happy memories you've had. Also even attacking all his Dino friends! :( so be sure to lock up this beast of a Dino!
In the wild, you can't do much with them. You'd think they'd be excellent for luring to bases, but it will prioritize all other Dinos over you, so it isn't worth the effort. Once tamed, the Giganotosaurus is the best method for hunting. Should you need to stock up on meat for breeding, raising, or just feeding, this is your best bet. Of course they're also just high damage Dinos too, so they're excellent for PvP, tanks with jaw of iron. Fair warning, when trekking across a map with them, take the flattest route possible, they're terrible in forests, mountains, and water. They also take fall damage very easily, so avoid jumps of any kind. Should you end up falling off of a cliff, dismount before hitting the ground and the damage will be avoided.