Maim is considered a stun and as such, shares diminishing returns with other stuns, such as bash, however it will not share diminishing returns with Pounce. The target can take damage without the maim being broken.
A four combo point Maim gives you enough time to heal yourself with a Healing Touch, or give your energy enough time to regenerate for a Shred. Also in 1 vs 1 you may have time to Prowl and Ravage or Pounce again.
A low combo point Maim is great at interrupting casts.
After a two to three combo point Maim you can cast cyclone safely, this gives enough time to Prowl.
Patch 3.2.0 (04-Aug-2009): Tooltip now specifies that the Interrupt effect only occurs on non-player targets.
Hotfix (2009-06-08): "When immune to the stun of following abilities, Maim, Bash, and Hammer of Justice will no longer cause player spells to be interrupted but they will still interrupt NPCs. Also, when these abilities do stun a player target, they will not perform an interrupt effect and lock out the affected magic school. As an example, if a Mage is channeling Arcane Missiles and is hit by Hammer of Justice, Blink will now be available as the Arcane school will not be locked out as it was before."
Patch 3.1.2 (2009-05-19): Rank 2 of this ability is properly considered a stun and can be escaped by Blink.