Suppose a client requests a floating license with a lease length of 1 hour. If client is done with it's work after 30 minutes, it should inform the license server, so that license is freed. If the client doesn't, the license becomes (zombie) useless for next 30 minutes as server assumes it is being used. After, lease time is over, server expects the client to send a refresh request, if client doesn't, license is automatically freed. Hence, zombie licenses are automatically freed up after lease time is over.