What is multicast snooping and why does it break UPnP/DLNA?

I have a server which, amongst other things, serves media over DLNA (UPnP) using mediatomb. Clients use *Simple Service Discovery Protocol* (SSDP) to locate the server on the network. I found that the SSDP discovery M-SEARCH queries were not being responded to and eventually tracked the problem down to the fact that the server was using a bridged interface which had *multicast snooping* enabled (because bridges have this enabled by default). I fixed my problem with echo 0 > /sys/devices/virtual/net/br0/bridge/multicast_snooping However, although this works in my situation, I don't understand what it's doing and if there are any implications that I am unaware of. Hence the question.... What is multicast snooping, why does it break SSDP, why it would be wanted and why it is enabled by default on a bridge, and what problems may be caused by disabling it because It's presumably enabled by default with good reason ?