Do I have to control Eos?

[chococo]

It exists for a reason yes, but not because its necessary to use it. the reason is FREEDOM.

You dont really need to, but if you want to be more useful, incase of failure which others or you cause, you should.

I wouldn't say it's entirely true to put it that way.
I can be a tank that doesn't use my cool downs. It's there but not necessary to use it. It's freedom! Would I gimp the party? yes. So would a SCH that doesn't control fairies.

If you can control even embrace to heal more frequently (if left alone fairies are a little slow), you can free up yourself to do other stuff such as putting up DOT.