This cvar sets the maximum FPS of a wow window while VSync is off (disabled). Just because you set this cvar to a certain value, it doesn't mean you'll see that fps depending on your machine's hardware.

Default Setting

0

This cvar defaults to 0 - which means it won't create a maximum fps, but the game engine has a soft cap of 200fps. However it can be changed to get better computer performance, or limit your FPS if your machine is getting close to overheating.

Possible Settings

0-199

0 

Set to wow's softcap (200 fps)

Changing this setting

In-game, type the following

/console maxfps setting

Alternatively, you can exit wow, open the Config.wtf file, and add the following line:

SET maxfps setting

Patches

Patch 3.3.3 (2010-03-23): Softcap decreased to 200fps 
Patch 3.3.0a (2009-12-14): FPS softcap 1000fps