If I head over to https://cesiumjs.org/ and zoom way in near either of the poles, ceisum will begin to endlessly make network requests for imagery tiles. I let it run for a while, watching the network in dev tools and I am up to over 5000 requests for tiles...
This is preventing our users from doing ship traffic monitoring in the Arctic because it slams the map server. It does not happen when zoomed in the same amount over another area of the world.
Tested in Chrome 62 and FF 52 but I assume it will happen in all browsers with the current demo on https://cesiumjs.org/.