It's got a very nice way of handling text size and other text "attributes". All the various kinds ("faces") of text are arranged in an inheritance hierarchy, so a change in the size of the text in the base of the hierarchy propagates to all of the text in the application (minus the size of the text in the title bar, which is of course controlled by the operating system).

So for example, to make all Emacs text (except the title-bar text) pretty darn big, you just eval the following:

(set-face-attribute 'default nil :height 200)