If you use LaTeX, then you probably have a bib file — a data base of all the papers and books that you have cited. It is much more efficient to keep one database in one location, than have multiple copies of it floating around your hard drive. (Or even worse, have different bib files created for different papers.) You might also have a few of your own style files, and again it is best to keep these in a central location and not have duplicates all over the …