They won't apply your VIP discount on something you buy with a coupon for 40% or 50% off. It does apply to sale items and full price items.
I asked a clerk if she would take my extra 40% and 50% coupons and use them for someone who didn't have any coupons since I couldn't use them, they expired that day, and she told me that store policy was that they couldn't do that. But she did put them to the side of her register and winked.