The difference between the best and worst classroom PowerPoint is vast, greater than any other classroom tools I've used. The teacher who uses it well will enjoy easier classroom management, more satisfied visual learners, richer classroom conversation, and will be, herself, a more satisfied teacher. The teacher who uses it poorly (which is to say, typically) will leave her students no better than when she found them and, in many cases, they'll be a lot duller.
In other words, PowerPoint is rarely value-neutral. Let's make it great.
Clipping is a handy way to collect important slides you want to go back to later.