People whose slides summarize their talks give two justifications for this practice, neither of which is valid. The first justification is that slides that summarize the talk help to remind the speaker what to speak about. The right way to remember what to speak about is to rehearse the talk in advance (as many times as it takes). You can also write an outline for yourself that you do not display. The second justification is to enable people to get the gist of your talk in your absence. People will rarely use your slides in this manner. If you really want to give people the gist of your presentation in a format that they can read by themselves, then write a summary separately.