I've been on connections where the ISP (AT&T) tried this due to an ancient backhaul where it grossly over-committed on bandwidth. The neighbors would have kids home after school streaming three netflix 4k streams, and we would watch our speeds tank. Some bizarre QOS config seemed to prioritize their connection over ours. It ticked me off enough I almost started deauthing their devices because I couldn't load a simple web page.

On the other hand, we finally got FTTH and it's great. So nice to have good speeds.