Some psychological insights have a great deal of practical importance. It seems to me that the ‘peak-end rule’ is among these. Essentially, the idea is that when remembering an experience like a medical procedure or a vacation, our recollection is strongly coloured by the most intense portion of the experience and by the ending. Sam Harris mentions this on p.77 of the hardcover version of The Moral Landscape: How Science Can Determine Human Values. It is also mentioned in Paul Bloom’s free series of psychology lectures.
The insight has practical value when it comes to unpleasant experiences. Harris describes how prolonguing the least painful portion of a colonoscopy (at the end) reduces how much pain patients later recall having experienced. It seems to me that the insight could also be exploited when planning pleasant activities. If you are setting up a concert, art show, or vacation, it seems like a good idea to include something that will serve as a positive and engaging emotional peak and to put some effort into ending things well.
Setting up a strong emotional peak could also benefit those hoping to cultivate romance. As mentioned before, people misattribute excitement unrelated to a person who they are getting to know. While it might be the scary movie or the rollercoaster that is causing your heart to pound, some part of your brain may wrongly attribute the feeling to the person who you are sitting beside.