On Mon,  3 Dec 2012 22:36:03 +0800
Cong Wang [off-list ref] wrote:

Fast leave allows bridge to immediately stops the multicast
traffic on the port receives IGMP Leave when IGMP snooping is enabled,
no timeouts are observed.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Hemminger <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <redacted>

I like the feature, and it looks like an oversight in the initial design.
Why is this not the default, adding more options obscures it.