Well, there is a difference, of course, between a building being “primarily used”—that means, presumably, the main reason that the building is being used is for that particular purpose—versus just “used”. “Used” could be someone using that particular building several times, infrequently, or just one time; whereas, “primarily used” means that the purpose for which that building has been built or established is primarily that use alone, and not other uses.
On March 9th, 2017. See this statement in context.