JohnEgan
I guess another question or answer would be what harm would having x2 on all the time do?
More calculations than needed so more of a CPU hit.
I am a big proponent of upsampling BUT only if it's relevant. The biggest effect is with processes that occur inside the box - amp sim distortion generation, limiting, synths with algorithms as opposed to samples, etc. One would think that if something oversamples already, upsampling wouldn't be necessary but that's not always the case.
I think the simplest solution is to listen to something upsampling and not upsampled. If you hear an improvement when upsampled, go for it.
This video will likely blow your mind...