The answer is "only occasionally", it's a nice way to bring focus to your subject without using a vignette or edges. The best images to use them on (in my humble opinion) are "portraits".
I am a fairly recent convert to textures, it was after seeing Jed and Vicki Taufer at WPPI Boston and in Vermont, seeing how they used them - in a very subtle way that enhances the photo (not over power it).
Let me share three images from Vicki that made me a texture convert.
(Click on any image to view larger & see more detail. They'll open in new window.)
