This read-write integer (1-65535) caps how many multicast groups the switch may learn purely from observed data traffic (data-driven learning) rather than from IGMP reports. Admins lower it on memory-constrained switches to prevent a flood of unexpected multicast streams from exhausting the group table, or raise it in video/IPTV networks that rely on data-driven learning. Setting it too low can cause legitimate streams to be silently dropped once the learned-group count hits the ceiling.