Symmetry - maybe I'm missing something but I think that the parallel channel tool typically provides the same benefits as measuring symmetry manually?  (except at the start of a new trend). On a related note, I've found that before a trend changes (on any time frame), the channel tends to break in the direction of the trend (so if a downtrend, price breaks below the channel)...and that is a high probability signal that a reversal is coming that will actually break the other side of the channel and start a new trend (time frame dependent). Look at the recent break of the SPY channel to the downside as an example. It just happened, but I've been monitoring it for months now and it does seem to be a pervasive phenomenon...