I am licensed in NYC and Nassau.
Technically speaking you need a permit for any work done in or outside of the house. I would think that more than 80 percent of people do not pull permits for small jobs like yours.
The reason to use a licensed contractor is that if you have problems with a contractor you will have some type of recourse. if you use someone unlicensed and they dont do a good job or dont finish then you are out of luck. Generally speaking I would would be worth the risk if the unlicensed guy was significantly cheaper so even if they walked off the job you dont loose too much. I would also encourage you to buy materials and only pay and unlicensed person as they complete work, assuming you do this route.