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.
I finally got around to doing my day skipper last year and on the course was a Russian who spoke English perfectly fluently but struggled with the technical terms that the rest of us took for granted. It probably doesn't help that sailing is one of those sports where the difference in terminology between British and American English is sometimes significant, for example I don't think the term 'kicking strap' is used in the US.
The knots I use most often even outside of sailing are the bowline and the round turn and two half hitches.
There is a very nice animation on the site for the Monkey's Fist (where I just now learned the finishing touch to deal with the loose end of the line).
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.