well third channels are used for nitro monster trucks with a reverse gear in the transmission. example would be a T-Maxx, Revo, Savage or an LST.

It's also used for electrics monster trucks and crawlers that would require four wheel steering like a Clodbuster style trucks or even a 2.2 crawlers that would have a a dig unit installed. Or even the Traxxas summit uses 4 channels (I believe) to lock the front and rear diffs. Even the old style Traxxas E-Maxx and the Tamiya High Lift uses the third channel to change the transmission between high and low gear ratios.

As far as radios go I have the dx3s IMO is a very good radio but it still lacks the features I want. The third channel is a 2 position only (servo goes left and right)in some applications like for crawling a 3 position third channel is needed for a dig (left * center * right) or for steering the rear tires.
Sorry if I'm confusing you and going off on third channel..... anyways I have never had a problem with glitching with my Spektrum system its been very reliable.