Why a socket is needed for each namespaces?

[wrongharry]

In https://github.com/LearnBoost/socket.io/blob/master/lib/manager.js from L642-L650

A socket is prepared for each namespaces, may I know why it is needed?

Suppose a socket is need when the client is on that channel.

For example, if there are five channels, if client1 only join the first channel, he/she will only need to in channel1 right, but now he/she is in all five channels, is it too much?