I don't know about Pieris, but Nemesias often benefit from pinching, especially the faster growing annual hybrids. Don't do it too often: the flower buds form on the growing tips.

Thanks Tug.

Yes pieris respond well to quite heavy pruning.

Thanks Steragram. When is the best time to do this ?

I guess straight after flowering but quite honestly mine doesn't seem to mind much. If you need to take it back a lot you could do it half one year and half the next - looks a bit odd but it gives the old wood chance to regenerate before you do the other half.