They're not essential because there are many people who make money without them. I know people who make money is trading who believe fibs are useless. I strongly disagree, I think they are the most useful thing in trading - if they are used correctly.
I've been trading for around 10 yrs and for most of this time I've used fib extensions/retracements are my main method of analysis and strategy design. I'll perhaps expand on strats another time but for now I'll say I am using fibs to determine entries, stops and targets. Often a combo of retracements/extensions.
Finding consistent ways to draw fibs is critical.
"If I drew loads of lines across a chart price would hit one of them. Loads of confirmation bias IMO" is a common objection of fibs (And many TA things). And if you're randomly drawing lines to be where you want them to be, this will not work. You need non-subjective ways of drawing fibs. This is possible. If you're drawing fibs from swing highs to lows ... there is only one high and one low. There are ways to consistently do the same thing.
I find the market reaction to fibs as inflection points to be spectacular. A very high percentage of the time they will be important for trend decision level. Note - "Inflection"/"Trend decision". This is not saying the fibs hold all the time, more that they will tend to hold or be important as a breakout. This is true of all basic theories such as retracements etc and also of harmonic patterns (And if you want to use fibs, learn about harmonics).
Many fib levels are useful for different things. They can help you determine important support and resistance levels well ahead of time and make trade plans around them - but it only works if you are consistent and honest in drawing the fibs.