Ironically, the one who signs somone as inviter is the one who is really "Sponsoring" something. There is no real sponsorship (unless some guild or indivifual freewillingly off the official system does something like that).
The benefit of inviting people is that inviter gets 10% of any credits his invitee buys. Invitee does not lose them but the system generates extra credits for the inviter. This is the normal promotion system used in the web scheme; get more customers = you get some benefits.