Martin, if you have a receiver such as the 3808 or the many other units that have auto calibration systems, then no, in my view there's no good reason to do the calibration manually. The auto calibration done with the receiver's built-in SPL meter and processor should be at least as accurate as using a separate external SPL meter to assist in making a manual calibration. The added factor of human error in the manual calibration would make it likely that any difference in the results would mean that it was us, not the receiver, that was "off".
This doesn't mean that an SPL meter isn't useful, and I frequently use my RS digital SPL meter to check minimum, average and maximum sound levels when I play various program materials.
