This gives you complete control of the way your page is displayed.

Well, not really. Twelve point type, a readable standard in printed matter, will be too large in one browser and too small in another. What the user actually sees is a function of the browser, the way the user has set the browser's defaults and the user's selected magnification.

There is a good argument for always using relative font sizes, such as

<font size='+1'>somewhat larger text</font>

These let your users control their own displays (adjusting for their eyesight, monitor size and resolution, and browser issues) and your website will display sensibly for each user.