Almost every caves, strong creatures can't follow with you. Even some caves need to go underwater to get useful resorces or trophy and dossier and again, most creatures that you are familiar usually are not good at diving and swiming. If they are good at diving and swiming, they are too weak to travel caves and underwater's creatures.
But after baryonyx released, no worries. It will keep your safe and help combat from almost every normal cave's creatures(high lvl megalosaurus will tough at night times, but it is weak at day times and still your bary can tanking few sec if you spend points on health for most.), even it can dive into the water endlessly if you have preparation about oxygen, coldness or scuba and still it will help help your combat from underwater's creatures.
Baryonyx are quick like Allosaurus and do just as much damage (but don't get a pack bonus). They don't use oxygen for swimming and can sprint in the water. Right click in the water does an AoE stun that lasts about 10 sec. Their 'C' is a... Taunt? They also jump and you can fire a weapon from their back.
It's like a small Allo combined with a Kapro, in my opinion. Useful on both land & in the water. Use its secondary attack while swimming to stun, attack, and harvest. Does NOT stun Cnidarias, though, so do not expect to overpower them.