I would tell you except... I don't have a classic controller and I have no idea.
Why would you even post in this thread then if you were no help to him, are you just trying to rack up posts???
To answer your question, well I'm pretty sure you're not talking about the home button, so I'm gonna hafta assume you're talking about that little clicky-thing at the top of the controller near the shoulder buttons. If you look at the back of the controller when you click that top middle button, some of the "apparatus" shifts. I think that's for attachments that you buy (for now only 3rd party) to attach the Wii remote to the classic controller so it doesn't dangle when you use it to play VC games.
I hope that helped.