The practicality of knots and their traits is what drives their use. When you deal with boats, you need these knots to perform and not come undone when you are not expecting them to (which could be dangerous). And you also need them come apart when you need them to.
Properties like that are what makes a lot of these knots so useful. Technically, you can get by with knowing only a handful. But there are a lot of specialized one with niche usages.
As a fly angler, in addition to the practicality of a given knots purpose and use is the practicality of implementing it in different conditions. There is often a lot of additional “tribal knowledge” on some of these knots, like the clinch knot is great but tying it with some hemostats speeds the process up and is easier when standing in a river. There is a great trick for tying a blood knot which makes it easy whereas doing it from the website would be nearly impossible outside in the weather.