Dean Collins worked that way in a specific system of his own that used multiple lights in a controlled studio setting and he taught that in workshops. He also shot Polaroid tests to make final adjustments. His incident metering method was a personal style and the methods he demonstrates should be taken as teaching his methodology, not as instructive of how an incident meter should always be used. He used either fill light or reflectors in a studio setting. He really doesn't take into account the intentional design of the meter dome that Bruce mentions. Collins was a nice guy, but he teaches a very specific way of shooting. None of the pros I worked for in studios went to his seminars when he was in town. They already knew how to light in a great variety of ways and how to use a meter. Collins drew mostly wedding and portrait studio folks, and he helped them a lot.

The Weston Invercone and standard incident domes were designed and calibrated specifically to be used pointed at the camera from the subject (or in that same orientation in identical light levels). Other methods may work if you know how to account for any necessary adjustments (or take other readings or adjust lights and reflectors to determine fill ratios like Collins does), but they are not using the incident meter dome as intended by the designers.

Case in point is Phil Davis' method of using an incident meter to find subject brightness range for an incident meter Zone System method. His method shows an excellent understanding of the characteristics of film and of incident reading methods. You'll notice, if you read his method, that the dome is pointed at the camera for metering light levels in both the fully lit and shadow portions of the subject. With Davis' method, incident readings are perfectly functional in a Zone System setting.

Incident and spot metering methods are both extremely flexible, and someone who doesn't understand them can get lousy results with either. Someone who does understand both can get great results with either. Special circumstances can make one method or the other preferable, but either can cover a great majority of circumstances.

Lee