Really, the only one good reason to tame one of these fishlike lizards is just it's perfect for traveling ;

It would remain invisible to every wild creatures, so, no one would agro on you

Plus, you would travel around at lighthspeed...

But the low health, due to low stats (low health, low melee damage), it's shitty for everything else

As it's an annoying taming process (sharks would not leave you, while you're just gaving food to the ichtiosaur), just don't lost your time on taming one, unless you are going to travel far