The contents of the file |preload.cfg| control the preloading of commonly used fonts. Preloading fonts speeds up the processing of documents but, because fonts can not be `unloaded', you should not preload too many; otherwise you may be unable to process documents requiring unusual font families.
The default file |preload.ltx| is produced from |preload.dtx|. It loads only a few fonts and these are a good choice if you normally use documents at the default, 10 pt, size. If you normally use 11 pt or 12 pt then the time for LATEX to startup may be noticeably decreased if you preload the corresponding fonts for the sizes you use. Similarly, if you normally use a different font family, for example Times Roman, |ptm|, then you may want to preload fonts in this family rather than the default Computer Modern fonts.