There are multiple reasons a teacher might make use of PowerPoint. One reason is that it makes a great creative and organizational palette for learners to use and they assimilate and internalize knowledge. However, the same things that make for great fun in cementing our own knowledge don't always make the best tools for sharing knowledge. One example is that PowerPoint animations have been shown to reduce comprehension in some cases.
One popular presenter, Larry Lessig, has adopted his own style of PowerPoint usage. You can watch an example of his style in this TED talk.