To quote the Debian Project Leader official page:
"The Debian Project Leader (DPL) is the official representative of the Debian Project. They have two main functions, one internal and one external.
In the external function, the Project Leader represents the Debian Project to others. This involves giving talks and presentations about Debian and attending trade shows, as well as building good relationships with other organizations and companies.
Internally, the Project Leader manages the project and defines its vision. They should talk to other Debian developers, especially to the delegates, to see how they can assist their work. A main task of the Project Leader therefore involves coordination and communication."