Assuming that you have a built in fax modem in your desktop or laptop computer, this is extremely handy, especially if your job is such that you are required to travel a lot and use a laptop. If you need to send faxes because you don't have access to Internet to send correspondence by E-Mail or the target of your correspondence does not have Internet acces but only fax access, this helps as you can correspondence by fax. Plus, your computer can double up as a fax machine allowing you to also receive important faxes without settig up another phone line. Just unplug your answering machine when you are expecting faxes and set your xp fax program for 4 or more rings to receive fax calls.
P.S External Modems/w faxing capabilities can be purchased fairly inexpsensively from E-Bay. If you don't have a fax modem for your laptop consider purchasing one as it is a good addition to any computer. Consider buying the External Fax Modem as it uses minimal if any computer resources and is compatible with linux should you ever wish to try your internet dialup with linux distros such as puppy linux.