Lossy encodings of media have tons of advantages - smaller file sizes, more portability, decreased bandwidth usage, faster buffering, etc. But one of the oft-tossed-away downsides is that videos lose a ton of quality upon encoding into lossy codecs.
To demonstrate this, here are a couple videos that show a source file undergoing compression on multiple iterations. It’s easy to see the degredation of quality even after the first couple iterations