It can capture the look and feel of what you see in dim or available light without the harshness often resulting from flash photography. It would eliminate the automatic exposure. If you manually controlled both, you would no longer have automatic exposure. If you see the warning symbol, you can redo your priority settings accordingly. Controlling depth of field.
Some people have a hard time holding a camera rock steady when pressing the shutter button.
Also, on telephoto shots or extreme close-ups, even slight camera movement is accentuated, resulting in blurred pictures. Use each to your intent - if you get out of bounds enough to possibly cause an over or underexposure problem, the camera will warn you. Comments in my sample pictures will tell you more about the practical use of exposure priority. Recommend using time delay shutter release to absolutely eliminate camera movement. Use for dim existing lighting conditions.