So imagine your scene is a city street at night. You have lights pointing at the façades of the buildings, streetlamps lining the street, and a police car with its headlights on, slowly driving by the street, checking out the pedestrians.
If it's a small scene for a cinematic, I would set the Mobility parameter of all the lights to "Movable" and forget about it. Now you can move the lights anywhere you want while you're building the scene, there is no pre-baking of the light so UE won't ask you to "build" your scene all the time, and everything will work in real time in the viewport.
But if you are designing a game, or this is a huge city and you want to be efficient, here is how you could go about optimizing the performance of your lights.
- I would set the Mobility of the lights pointing to the facades of the buildings to "Static" because I know those lights are not going to move, and no moving objects are going to pass under those lights.
- I would set the Mobility of the streetlamps to "Stationary" because I know those lights are not moving, but I want the pedestrians who walk under those lights to cast shadows onto the ground.
- Finally, I would se the Mobility of the car's headlights to "Movable" since the car is moving and I want any moving object that passes in front of the headlights to cast shadows.