There are some voucher codes on different websites that can be used only by website members. These voucher codes are often used as rewards for the loyalty that different members can have to a website. This is something that is kind of like giving members preferential treatment.

This does not mean that these promotional codes have to be off limits to non-members of different sites. A person can easily sign up to be a member on a site and then use discount codes on it. Memberships to be a customer on most sites are free and very easy to get.