The leader role (TL4) is manually given, and is given on a basis of trust and that the person wants to help the forum and community. In addition to the extra permissions and powers they are able to have on the forum (members have some limited powers as well), they have a lounge area as well.
Aside from that the main point of the leader role is that its for people who, embody the community for lack of a better phrase. We want to do more with the role and think leaders can help shape the community. Things like @kewldude007’s giveaways that he has organised in the past for example. One of the things we want to do is have leaders help make those kind of things happen more often, if its just helping direct the forum to organising an event or large discussion or topic, etc.