As per the Quora question above I provided the following answer :
It depends largely on your audience and type of talk. But one thing I have noticed over the years is that not only from real world experience but from those who study such things, is that each slide should VISUALISE the point just made. That is, a single graphic presented just as you finish your point. Give your audience a chance to see and understand the graphic and then let them ask a question or two about that point and the graphic. Generally you don’t combine text with graphics. But if it is unavoidable be prepared that the audience can see the text. Also make ALL presentations as short as you can. If you can make your message in 1 minute do so!