Knowing fundamentals and valuations helps keep you away from bubbles that will pop and take down a ton of investors. For instance, Beyond Meat (BYND) https://finance.yahoo.com/quote/BYND/key-statistics?p=BYND
It's fundamentals are horrible. Little in earnings (especially relative to their supposed size/market cap, even after the bust). Very little cash. Insane forward P/E, etc.