I don't like the animation on the website. I'd expect stationary satellites, not moving criss cross around the earth. Or will they not be stationary? This is confusing..
The animation is accurate. To stay stationary, a satellite has to be 35000km away from the earth, these will be about 500km away. They will move very fast across your line of sight, but have very low latency.
It helps with load balancing. Google Bloon planned to automatically geographically appropriate satellite clusters based on real-time demand, so I assume there are similar plans for Star-Link.