This snippet is for when lamers join/part your channel , it stops it from them doing it again :o)
Well first of all this isnt a flood protection, since it bans on the first sighting, so thats not a valid reason. Second I find it quite strange if i get banned somewhere just because i joined the wrong channel. And on top of that, the people that will get banned, how high do you think the chance is that they will ever return to that channel, probably nihil to zero