Holy cow, I wrote a book!
A customer asked,
Is there a way to turn off Full Window Drag on a single window?
I have a resizable control that I would like not update itself while resizing.
It so happens that I wrote a sample program ages ago to illustrate
how to do this.
You can find it in the Platform SDK under winui\fulldrag.
The source code is also reproduced in
this Knowledge Base article.
In addition to deferring painting, you may also want to defer
layout if layout is expensive for your window.