Depends on what NAS; mine has some substantial benefits. (I have a Qnap 4 bay:
http://www.microcenter.com/product/4..._TS-431_Server, often goes on sale for 200$ or less. Picked mine up for 150$)
I can access it from anywhere - even when i'm on the road. It will run a PLEX server for you (and an iTunes server if thats your thing), download things for you (has a torrent client and several other apps, including ftp downloads), transcode the video into a format/container of your choice after it downloads, all sorts of other things. It also uses way less power than even a small computer left on, and has apps for most tablets/phones that you let you access the video or audio or other files from wherever you are in the world securely, and it will automatically transcode the video to make it better for streaming across the web.
For 150$, it was a no-brainer. And adding more storage is super easy, and if you need to remove an old disk, as long as there is enough storage on the other disks still in the unit, you can tell it "im removing drive 1 to replace it" and it will intelligently store all the data on drive 1 on the other disks, and when you put the new disk in, automatically move the data back.
It also has smart RAID features, and features that mimic a raid but arent, all sorts of stuff.
Well worth it, IMO.