This parameter controls the internal rule queue size. In general, the bandwidth manager works so: an intercepted network packet is either placed into the queue or is sent directly with no delay. If it is placed in the queue, it remains there until available bandwidth appears. If the packets come at a high rate, but the manager is unable to send them from the queue due to set limit, the queue may overflow. When it it overflows, any incoming packets directed to this queue are dropped.
This is almost impossible sutuation for stream oriented protocols such as TCP, but still possible for UDP and other datagram oriented. There is no flow control for UDP and the queue may reach its maximum size. To avoid memory overflow, the packets are dropped.
This value (max size) can be lower if you have a lot of rules and a little memory and vice verca: it can be a higher value if there are a few rules and there is enough RAM in the machine.