Getting the VIP card costs you nothing at all. You don't have to use it.
Obviously, if you have a 40 percent coupon it would be more sensible to use the coupon. Equally obviously, if you don't have a 40 percent coupon, getting at least 10 percent is something instead of nothing. And, since the 40 percent coupons are only good on one item, if you are going to buy several other things, the 10 percent is good on those.