I think it all depends on what age your audience is and what your topic is about. If you have an older audience that generally has a longer attention span and your topic is old television sets, you probably would not need many slides. With a younger audience, their attention span is shorter, so a few slides with big graphics could keep them engaged. Generally, I am for the use of slideshows during presentations.
I agree, it does take some discernment to choose if you will use slides and how you will use them.
I did not take into consideration the age of audience may effect the impact of a visual aid, good points.