In your example, I guess you are reversing the 2nd signal so if the signals are the opposite. "Adding" or convolving them results in a zero? i.e. if the signal

In your example, I guess you are reversing the 2nd signal so if the signals are the opposite. "Adding" or convolving them results in a zero? i.e. if the signal is a (+)slope /, convolving it with a reverse of that signal \ = 0 In this sense you are leaving the difference between 2 signals.