Emp is a package for encapsulating MetaPost figures in LaTeX: the package provides environments where you can place MetaPost commands, and means of using that code as fragments for building up figures to include in your document. So, with emp, the procedure is to run your document with LaTeX, run MetaPost, and then complete running your document in the normal way. Emp is therefore useful for keeping illustrations in synchrony with the text. It also frees you from inventing descriptive names for PostScript files that fit into the confines of file system conventions.