The unban room command with no arguments will cause services to unban you from that room. Unbanning a nick will cause services to unban that nick, and unbanning a mask will remove a ban for that mask. The * is used to remove all bans in the room. AOPs and above can unban themselves, other nicks, and masks, but only SOPs and the founder can use the * to remove all bans.
/msg chanserv unban #webmaster
/msg chanserv unban #services *
/msg chanserv unban #webchat mark
/msg chanserv unban #conferenceroom *!jennifer@*.webchat.org
The unban command is primarily useful for unbanning yourself. If you are outside the room you cannot remove bans manually. However unbanning a particular nick can be useful if you're not sure how that person is being banned, services will do the work of figuring out how to unban the person. Unbanning all is a convenience, since any op could manually remove the bans, but it might take a lot of work. The command is restricted to SOPs because it is powerful, and if an AOP started manually removing bans, others would likely notice.