Their use is very limited due to the fact that you can only use it at night. During the day, if you keep it awake, it's stamina will drop very fast and upon reaching 0, it will start gaining torpor very fast which ultimately leads it to fainting.
If you get stuck out during the day, you can stop and set it to sleep to regain stamina and reduce torpor and hopefully rinse and repeat until you can get home. Be very careful if you carry it with flying mount, if it sleeps or faints you will drop it.
In PvE you are unable to pick up wild dinosuars, which limit's its use even further.
Even at night, while it's attacks are powerful, it isnt a first choice simply due to it's stamina. While longlasting, it regains stamina painful slow, keep it in mind if you need to flee!
The devs should add a command for singleplayers that the Megalosaurus can grab creatures on it‘s own without attacking them so the player can knock the dinosaur out easily in front of him (through a command like turret mode on the chalicotherium)