What happens when I delete system fonts?

I use fonts a great deal and the pulldown list of hundreds of fonts really slows me down. Even when fonts are disabled with Font Book some applications still find them and they show up in pulldown lists. And, as we know, Font Book won't delete system fonts. It's not just fonts in the languages I don't use, it's also some of the English fonts.

So, what will happen if I delete system fonts directly from the Finder? Will the computer still boot? What kinds of problems could I expect?