The license is only needed if you want to transmit. If you are not interested in talking to random people, there is a lot of fun to be had from just picking up signals and listening. There are hobbyists who enjoy picking up distant AM radio stations, listening to all kinds of voice or machine traffic on shortwave, tracking aircraft by their beacon signals, or just listening to local police on scanners.

As a listener myself ("SWLer") my next project is to make a radio to pick up telemetry from small cubesats.