how useful is the Faithfull Steed feat in general?

I am thinking of making a champion Of the Pale Horse, and because of obvious reasons, I think that I should take the Faithful Steed feat, but I have some questions about it,

the first is how do you manage the Mount? can you summon and unsummon it or do you have to bring the horse everywhere you go?

And in general, whats the use of a mount? how often do you find yourself needing a mount in the games you play?