I haven't read any of the preceding answers yet, so they won't bias me.
A Want, to me, is fair game for absolutely anyone to state, at any time, subject only to the idea of "good style" (don't do one after another). For instance, I wouldn't be embarrassed to post a Want to try a particular juice or piece of HW (as a loaner) -- absolutely not a Need, I can absolutely afford it or wait to try it, but as a good community member it's fair to have a Want pop up now and again. I may have heard a lot of good things about a particular juice, am on the fence about it, Want to try a couple ml.
A Need is something that should only come up if someone is trying to do something that they cannot cover, and that's directly related to themselves or someone they're immediately trying to help. Bucks are really tight, I just lost a battery and can't afford a new one with shipping at this point, I Need an xxx battery.
The similar concept pops up in multiple threads here -- this forum area works like a virtual coffee shop, people shooting the breeze, trying to help each other on different things.
Just my opinion, but opinions are like noses -- We all have them, and they all smell
Edit: Now that I've posted, I read the earlier posts. I totally agree that if someone fulfills a specific Want for me, I shouldn't accept others offering exactly the same thing. Now, I do mean exactly the same thing -- someone recently posted a Want for coffee flavors, and several of us offered them up -- it's fair to accept several different flavors from several responders, for a generic Want-to-try, nothing faintly wrong with that, since the request was to try different things of a general type.