I see now that the original post was unclear. What I meant by "good exit signal" was something that tells you the market has most likely just put in a high or a low. In such a case, you then automatically have an entry signal the other way. A lot of traders who are long will just get flat when they get a clear short signal. Because they have a long position, they just think about avoiding the loss, and aren't in the right frame of mind to then reverse and seize the profit available. I agree that if you are just taking profits, with no view on the market subsequently, then reversing does not make sense.
you are talking about two different situations. being in a trade and getting an exit signal (for me) doesn't always lead to a trade in the other direction. maybe a trailing stop was triggered and few moments later the market picks up the original trend. but an entry signal in the opposite direction to a pos. is of course a good exit signal.