Hello Stefanio
There are several reasons why we would want to filter IGMP packets. The most basic and important reason is to allow for a network to function more efficiently. The details follow:
IGMP filtering allows users to configure filters on a switch virtual interface (SVI), a per-port, or a per-port per-VLAN basis to control the propagation of IGMP traffic through the network. By managing the IGMP traffic, IGMP filtering provides the capability to manage IGMP snooping, which in turn controls the forwarding of multicast traffic.
When an IGMP packet is received, IGMP filtering uses the filters configured by the user to determine whether the IGMP packet should be discarded or allowed to be processed by the existing IGMP snooping configuration.
The major purpose of this is to reduce the number of packets that have to be processed by network and end devices and as a result free up their resources and make the network more efficient.
I hope this has been helpful!
Laz