To indicate to another that you wish to cease discussion on whatever the active subject may be.
Person #1: "I don't know what kind of flowers I want at my wedding. I like lilies, but I also like carnations. Carnations are probably too 'cheap' though. Oooo... what about tulips? Aren't tulips great? Are they even in season though? I would totally die if I could get tulips. Or maybe just lilies. Those are kind of classic, huh?"