I don't use fib retracement levels much, but when we get a big move up or down I've found they can be quite useful for determining where a pullback or rally may reverse. We just had a great example of how you can use these retracement levels for practical trading purposes. ES and NQ both sold off in early August before retracing the entire move shortly after. After the recovery and pullback, we had a well established range to use for fib retracement. We can use the low from August and the high from late August before the early September sell off.
By default on most platforms like TV, you will have 5 retracement levels. In my experience, I have only found the 38.2%, 50%, and 61.8% levels useful so those are the only ones I put on my charts. We got a perfect 50% retracement on ES before a 200 point bounce, which also coincided with 5400 and other support levels. For NQ, we have a perfect 61.8% retracement, which was also near where the sell off in early August started. There was a lot of reasons to think we may have support in that area, but fibs were a great confirmation on their own.
This is another very simple strategy you can use to optimize entries and exits, but you don't want to overuse or overcomplicate these things. You need a big rally or dump like we saw, there needs to be volatility and a solid range established. Once you have that, you can begin to look for fib retracement levels that coincide with your other support and resistance levels.