The areas we use HDRIs for are: textures for CG models, sky domes as reflection maps, sky domes as HDR lighting map, and live action backgrounds. For textures, we usually only need three exposures, since a building wall, for instance, doesn't carry such a high dynamic range to warrant more.

For sky lighting maps, we definitely use 7-9 exposures, same for reflection maps. For live action backgrounds (meaning the background for a greenscreen or bluescreen shoot), we usually use 3-5 exposures.

We wouldn't necessarily use a tone mapped file as an actual background for a greenscreen shoot, since that would look fake. But I like to have the range, so we have more leverage in adjusting our backgrounds and playing with the lighting to make it more dramatic.