How often do you use tin foil and what for?

Older (or cheaper) model ovens don't have the self clean cycle.  Sometimes, it's just one of those old habits that people do, even though they may have a self cleaning oven.   

Yeah, I've always done it.  My new oven actually says in relief "Do Not Put Foil on Oven Floor." (paraphrased)  I'm probably going to do that anyway because I always have.  I have a self-cleaning oven but take the foil out before using the self-clean feature.