You'd use RWS if there's more than 10 things to track in front of you (say 5 friendlies and 5 enemies). It should display up to 40 things, but as others have pointed out, it doesn't do tracking. So you have a dot, but you won't know which direction they're headed, you just have altitude. The good thing is, you can know which way they're pointed with the Link-17. So, if the awacs can see them you can see that on your SA page. You can get more range from RWS than other modes, but that's about it.
The radar itself should be able to calculate RCS (its listed as a feature of the radar itself) so you could theoretically identify which airplanes you're seeing, but they didn't put it in the game. Also RWS is supposed dto go into STT once you lock a target, but that doesn't seem to work well currently. STT is better for keeping a lock on a wildly maneuvering aircraft, its unbreakable. TWS is supposed to be easier to break (ex: if the plane goes into a steep dive or does a quick turn) but it's overperforming right now.