Well, there have been a number of people who've edited it wrongly and lost the ability to become root full-stop, and had to reflash.

Also, I've not yet seen a clear reason why R&D mode should be disabled anyway. Leave it enabled, unless you don't like spanners & green text when booting.

50p (about 92 cents) to anyone who can convince me why R&D mode should be disabled; after editing /usr/sbin/gainroot to disable the R&D check.