Any non member who pays the daily entrance fee is a temporary member for that day.
It is to comply with venue and state regulations, the same as the requirement for you to show valid ID with an address that matches the one you write on the registration form.
It satisfies the state requirements for holding auctions on premises that do not have a permanent licence to do so, and gaming requirements for private tournament play (for those rooms that operate under the letter of the law anyway - some who haven't have been heavily fined).