NOTE: Will ONLY work with Carbine's (Vanilla) TargetFrame add-on! If you are using a replacement, this thing will not work!
The little animated 3D portraits actually cost you a little bit of performance. This add-on allows you to freeze or hide those 3D portraits. If you aren't CPU bound, you can actually get some of the "lost" FPS back by freezing or hiding them. Also useful for those who find animated portraits distracting. Depending on the amount of these 3D portraits shown on the screen, the gain can be very noticeable. But don't expect miracles.
Either use the pin button, or write "/fp" to chat and hit enter. There are 4 modes (none, frozen, hidden, both). Difference between frozen and hidden seems to be minimal to zero, but added the extra options nonetheless. Note that, when the portraits are hidden, you cannot click on the frames; freeze (default) is thus suggested.