They can speed up and jump out of the water, making big splashes when diving back in again. Obviously for fun. They won't just float under water, and their mechanisms of movement have evolved in their environment, just like ours did for us.

I don't see your point? Not seeing the forest because of all the trees?

Octopussies have fun moving in weird ways, too. Also exploring, and making fun of captors!

Birds...did you know that their five feathers on the ends of their wings are the equivalent of our fingers, neurologically/network-wise? They sense the currents of the air with them.

Whatever. I think, no matter which species you are belonging to, it can be good to have these systems in more or less autonomous action, moving by themselves, while having a somewhat detached mind, soaring along, thinking about other stuff than the usual chores.

Edit: Maybe something like micro-dosing a little bit of 'Runner's high' by walking aimlessly?