Displacement effects on FPS?

[WaxyChicken]

I'm making a large outdoor map.
What effect do displacements tend to have on FPS?
avoid at all cost? use sparingly? OK just don't over do it?

[Stiffy360]

per-poly, it's actually cheaper than brushes since it's rendered in batches. Just make sure to use it smartly and don't overdo it.

[WaxyChicken]

thanks for the FYI stiffy.