Questions on Chapter Titles

Another question for the Thin Man today: Why do you name your chapters instead of just numbering them?

Why? Why not?

Seriously, why not? Whether the chapter is headed with the words "Subject Real" or "Chapter One" it's still the same amount of space in the book and the same cost in the project. That's the way I look at it; those words are a chance for me to add value to the book with no additional cost to the reader or the publisher. Plus, unlike the main narrative, chapter titles (or headers or whatever you want to call them) can be slightly non sequitor and sometimes you can do more with allusion than direct illustration. For example, the chapter "Dante's Fourth, by Gaslight" in "Calamity's Child". The reference to gaslight presets the reader's mind to Victorian imagery and the fourth circle of Hell in Dante's inferno was reserved for hoarders and wasters. Themes and images are set before the chapter even begins. Obviously, the technique of naming chapters doesn't work for every book but, if it can be done, I see no reason not to do it.