Sarah has written a really useful post about the different roles animation can play. Naturally, I was really happy to see her talking about the impact on perceived performance:
Animation also aids in perceived performance. Viget conducted a study where they measured user engagement with a standard loading GIF versus a custom animation. Customers were willing to wait almost twice as long for the custom loader, even though it wasn’t anything very fancy or crazy. Just by showing their users that they cared about them, they stuck around, and the bounce rates dropped.
In most cases, I’d argue, it would be even better to provide some sort of feedback to the user about what is happening in the background, but the same general idea applies: taking the time to design for when processes take too long is important.