When I'm reading the code I need to understand what it does, the underlying characters are just a medium. I can see way quicker that a complex boolean expression is wrong when I see ≠ instead of != and ⪖ instead of >=.

I do agree with the Butterick that when presenting code to others, for example as examples, the ligatures are a big no, because in this case you actually need to see what characters you need to input.