I currently using mecanim for the animations,
what I want to achive is start animation by state ( int).
But then I need to connect each animation with transitions to all the others
and its getting kinda messy and not comfortable when adding more than 3 states.
They offer some nice ways of grouping lots of animation states together, and help keep your Animator workspace a bit less cluttered, as well as simplifying code.
The youtube Mecanim tut goes over these quite well IIRC: