After auto cal is performed, the receiver offers an option for calibration matching. The feature is not well described in the manual:

Yes: Expands the sweet spot for the viewing position and allows you to enjoy more natural sound by trimming the wavefront for each pair of left/right speakers.

Can anyone explain in more detail exactly what this function is intended to do? Is it some kind of single-point equivalent of multi-point calibration, where several measurments are taken to create a better result over a wider area?

The feature cannot be switched on or off after calibration is performed, so it's difficult to do a direct a/b comparison. You have to run auto cal again in order to enable/disable it, which is frankly quite an odd interface choice.