In busy channels you might not be interested in all the joining, parting, quitting, and renaming that goes on. You can omit those notices using C-c C-o.
You can control
which notices get omitted via the
rcirc-omit-responses variable. Here's an example of
how to omit away messages:
(setq rcirc-omit-responses '("JOIN" "PART" "QUIT" "NICK" "AWAY))
Notice that these
messages will not be omitted if the nick in question has recently
been active. After all, you don't want to continue a conversation
with somebody who just left. That's why rcirc checks
recent lines in the buffer to figure out if a nick has been
active and only omits a message if the nick has not been active.
The window rcirc considers is controlled by the
rcirc-omit-threshold variable.