With video, you get 30 images per second, every second. So fast calcium transients - you see them. Microtubule dynamics - you see it. Blood flow - you track it. With video, you simply see more.
Video is Easier to Use Video is intuitive and easy to use when compared with digital cameras.
This means you spend more time running experiments and less time figuring out the complexities of your hardware. Part of this ease comes from the real-time video update, which makes focusing natural. But it goes beyond that. Video cameras are just intrinsically simpler than digital cameras. There are no shutters, no strange settings, no proprietary interfaces.