What are dfont files? Do I need them?

A dfont is really the same as a Mac TrueType font except its data is stored in the data fork instead of the resource fork. The dfont file format works only in Mac OS X. It was created for users who format their drive as a Unix File System (USF) since USF doesn't support resource-based files. As long as you're using Mac OS X or UNIX, it's fine to leave these fonts as dfonts and not convert them to Mac TrueType.

When an operating system other than Mac OS X or UNIX encounters a dfont file, it won't read or work with that file at all. So if you still use OS 9 or Classic versions of programs, or if you use an old RIP (Raster Image Processor) that runs a pre-Mac OS X operating system, you need to convert your dfont files into Mac TrueType files.

Mac TrueType fonts are neither better or worse than dfonts; they are the same font stored in different file architectures. You should see no differences in kerning or glyph quality between a dfont and a Mac TrueType converted from that dfont. The only real difference is that Mac TrueType is usable by Mac OS X and pre-Mac OS X computers while a dfont is not.