How much do you need exposure-meter in the photography? (Actions)

A professional photographer has been recently associated, first of all, with a large SLR with "telephoto lens" and a large semi-circular exposure-meter on his chest. Today, most of the digital cameras initially have a built-in exposure-meter and usually do not require free-standing measuring instruments. But how much do you need free-standing measuring instruments at all, and when it is reasonable to use them?

Free-standing measuring instruments help the camera to perceive luminous flux properly and without distortion, and to "fit" the image to the lighting parameters. Article about portrait lenses tells about these features and also about some characteristics of the photographic lenses.