Generally speaking there's often a perceived difference between a DP and a "shooter" and it has to do with controlling the lighting in the environment one is filming in.
A "shooter", i.e., news gatherer, event videographer etc., may adjust their camera settings to the environment and leave it at that. A DP, on the other hand, will adjust the environment and the lighting, to the camera settings he or she has chosen for their camera.
The main tool used to help assist a DP in this mission of adjusting the environment to their desired lens and camera settings is their light meter. Cause it measures light falling on and reflecting off surfaces in frame.
So there are appropriate situations to use a light meter, like when you're shooting a music video or movie, and other situations where you'll get some awkward stares if you suddenly pull it out and start metering, like a live basketball game for example.