Animations can be used in a variety of contexts within a presentation, but one of the most common is to simply control the rate at which information appears to students. So, for example, on a slide dedicated to discussing four aspects of a given topic, the relevant text and images can be made to appear gradually, so that each aspect is discussed thoroughly before the next even appears. The alternative, dumping all the information to the screen at once, and then working through it verbally, would seem to have the potential to distract and overwhelm the audience. So, this seems to be a situation where animation should clearly help.
What is interesting about this is that the study wasn’t looking at complicated animations, but mostly at having certain lines show up on the screen. They used the same slides (I would have though people who use animation put too many things on a slide, but this blows my theory). Maybe it helps to be able to see the entire context for longer, so you get more of chance to process what’s on the screen.
This kind of thing is hard to study, but it certainly makes one pause about current Powerpoint habits.