caveat on my bill always says 100 miles, you drop the bike before you have no comeback. its there for a reason.
as recommended by all the major manufacturers, its primarily due to the release agent used in the moulds and secondly , to allow for seating on the beads correctly. I have known painted alloy wheels with excessive old tyre lube/soap used for fitting build up or corrosion of the ally cause leaking. you wouldn't want at higher speeds.