We have a VF0 purchased in 2000, the X and Y covers have never removed to clean out chips. They were removed to check on a ball screw noise and there was not any significant build up of chips. The Z covers were removed to repair damage and no chip build-up was found.
However, we also have MiniMills and these are really bad for packing chips up behind the Z axis covers. I think they need cleaning about every three years or so.
An open mind is a virtue...so long as all the common sense has not leaked out.