This page is part of the web mail archives of SRFI 62 from before July 7th, 2015. The new archives for SRFI 62 contain all messages, not just those from before July 7th, 2015.
FWIW, I find them to be quite useful to comment something out and bring it back again. It's true, I can do the same with #| |# and a few more keystrokes (removing it seems to require more than putting it in), but #; seems to hit a sweet spot for me. just my 2c, Robby