I know that sharpening is best done as the very last step. Should it only be done AFTER the final sizing. This means keeping a master image that's unsharpened, then when you export the image for a target medium, and scale it down as you do for the web for example, sharpen the final scaled image only.

OTOH, do effects like smoothing and sharpening work best when they have the maximum pixels to work on - which would indicate that it's best to do ALL processing before scaling down. But I have read that scaling an image down to a smaller size has a smoothing effect due to the averaging/interpolation of the pixels. Does that mean that SOME images might beneft from a final retouch? maybe a slight sharpening if the smoothing is too much, and/or maybe a slight smoothing in some areas if artifacts from the scaling are present?