Some prefer to listen to just the police and fire, while others are primarily interested in commercial avaiation.
Scanners are also very popular with boat and train watchers.
For some elderly shut-ins, scanners help provide the much needed feeling of knowing what's going on in the community around them. Unlike conventional radio or television, it is impossible to know what might happen next, and there will never be a commercial time-out just as things heat up. Scannists can listen to just about anything that interests them. As mentioned above, some folks prefer to listen to specialized communications such as railroads, while others prefer to listen to anything and everything. If there isn't much action with the local police department, maybe it's getting hectic at the airport, or traffic is starting to snarl up on the Turnpike.