Excellent advice. Though applicable Shimano Service Instructions of that period do often cover how to install Biopace chainrings, not everyone is going to have that kind of documentation readily available (and perhaps won't know where it can be found). Documenting the orientation in some way before removal thus seems a very good idea if you don't have access to period Shimano documentation concerning Biopace, or if you've installed them in an alternate configuration that you like better.

Added: turns out that the older Shimano docs covering Biopace installation are harder to find than I remembered. If anyone's interested in having a copy of those instructions for future reference, do an internet search for "SI-T-30A-000-00-ENG" and choose the entry from "si.shimano.com" covering a number of FC-M### cranksets. That document explains how Shimano recommended orienting Biopace chainwheels during installation.