A free membership allows a player to play only 20 games simultaneously and when this limit is reached, new games cannot be started until the number drops below 20.
Higher membership levels solve this problem in the following way:
(hide) If you want to play a game with an opponent of a similar level, you can define a required BKR range for a new game invitation. Then nobody with a BKR outside this range will be able to see/accept it. (Katechka) (show all tips)