Gyro lets you set up macros (lists of commands) to be run whenever you join or leave a raid, for convenience or laziness. You can, for example, enable raid UI mods only when you're actually in a raid, disabling them when you're done.
It's easy to set up: put commands you want to be run whenever you join a raid in the GyroStartRaid macro, and the commands you want to be run whenever you leave a raid in the GyroEndRaid macro. (Gyro creates these macros for you automatically.)
For example, if you want Hear Kitty to only operate when you're in a raid (not sure why, but whatever...), you could use these macros:
More details are in the readme file that comes with Gyro.
Additional changes for Mists of Pandaria and patch 5.0. This version of Gyro will not work on old versions of World of Warcraft.