One of Addon Control Panel's best features is the ability to manage other addons in-game, without needing to log out and back in. It also has several other features, such as custom profiles for each character or different UIs (User Interfaces) for PvE and PVP, as well as a utility for limiting "clutter", by organizing multi-part addons and libraries neatly and logically. I consider it to be crucial for anyone who uses more than 10 addons.
Not much else can be said about the addon, except that it is simply awesome and you should get it. It is definitely one of the best addons for World of Warcraft.
The custom profiles are accessible under "Sets". They are easily configurable, allowing for you to make different setups for several PvP classes on Warsong (instant level 85 PvP only), for example.
Commands:/acp - show and hide the ACP window
/acp disableall - disable all addons (except protected and ACP)
/acp default - restore the enabled addons to what was enabled last time the UI was loaded