RVSM requires VS not to exceed 1000' FPM if traffic is 1000' higher/lower and within 5(10?) miles.
Some SOP masochists think the world comes to an end if you touch the VS selector. But how do you comply with RVSM requirements if the SOP police say "don't touch"?
VS makes nicer level off's. Allows you to select the VS approaching level off vs. the rate selected by the programmer who never piloted an a/c with 1/3 of the passengers afraid of flying.