The notable benefit to the ttf format over bitmap based font types is that TrueType data is proportional. It can be scaled to any size, and still look perfect. This also means much smaller file sizes, because bitmap formats require images for each desired font size. On the downside, rendering ttf's is a much more complex process. Also, many systems don't support them, or support them poorly, as anyone who has ever made an attempt at getting freetype to work with linux will tell you.