Generally, postscript is used for vector drawing, page layout and prepress application, as well as for its strong typographic capabilities. If you're working with PDFs, postscript was the foundation that PDFs were built from.
If you're not really using postscript now, I doubt that you really would delve into it unless you were getting into signage, advertising and the like. If you're using a lot of Adobe Illustrator and InDesign, or Quark Xpress, you definitely want to print to a postscript device over other imaging models.