Patch LOD. Yup, its true. Try making a gigantic map with a curve patch at the other end, take out sniper rifle, and scope it while steadily moving backwards. You’ll notice the patches lose detail constantly.
(Ever notice how when you make a really small patch in radiant, it appears as a square but ingame its a circle?)
For example, in my recent map I used all patches for a reason
- Very smooth and didn’t need phong shading and
- Since its huge and open, patches visible on the other side of the map wouldn’t hurt the fps.
http://jediknight3.filefront.com/file/Industry;98462 if your interested.
So ya… great for some things, like I used, but bad for things like roads, puddles, etc. In that same map I posted, I tried to make puddles in the floor by lowering the ground and putting a patch over it, deforming it, then putting a water brush overtop. It worked great, until I backed up a little. Even worse when I got to the upper level and looked down, where it was nearly just a square of water! Had to ditch the idea. 
Another great use of patches is in combination with PolygonOffset. You can do things such as hanging rugs
( http://www.chromecreations.co.uk/3d/filefront/02_serenity_progress42.jpg ) and circular patterns on the floor in a different texture, such as something shiny.