Relevant discussion of the past:
http://www.wowinterface.com/forums/s...ad.php?t=46740
Basically, when you move an element (SetPoint) constantly it's a big performance drop, which you only ever really see with nameplates (as every other UI element is static).
In that thread we/they concluded that hiding the frame(s) prior to moving it then showing it again when done moving would result in a much better performance, and no visual difference.
Once I have access to the beta, taking a look at the nameplates will definitely be one of my top priorities.