If you, say, were a-cackling away at work when the grove first moved, and perhaps registered your account, right there at your work email...
and say perhaps didn't want to keep it with your work email, and instead would rather the grove cackled to your home email.... let's just say this could be you... you want to change it in your usercp.

CHANGE IT AT HOME... or for the rest of the day you will be unable to post, as it makes you reclick the registry link from the new email addy, rendering you unable to cackle while at work that evening =(

do not let this be you! i'm sure the staff has stated this in less words, more eloquently, much more clearly elsewhere, but hey, who can possibly read everything while at work?

cackles!