How can I setup Events + Social apps for clients

Do you know:
1) If I setup the Facebook, Twitter, Google + Apps, what that is needed for? Is that so users can RSVP to events with their social accounts without having to signup to the wordpress site?

2) If I create a site and setup this plugin with the social apps setup I would be doing so via my own Facebook account and Twitter and Google plus but then if I sell this site to a client do they have to do the Apps ID setup all over again or how would that work?

If they don't re-setup the social app id data themselves that would mean they would forever be tied to my apps I created in FB, Twitter etc right?

What's recommended?

Thank you!