Yes, if you need to rotate with the terrain, otherwise not. I used one here to get some angled trees. But that one won't influence render time.
With a compute terrain to compute the whole terrain, especially after a lot of nodes it may add significantly, so I try not using one, if possible.
Okay, updated iterations. I might put something together for NWDA, just like the river preset, with masked areas to fill in. But it would need some more EasyLogic and cleaning up