When I’m writing, I often find it useful to be able to quickly see where else I have a certain word in the text. In Notepad++ this is called Smart Highlighting - all you have to do is select a word, and you’ll see all other occurrences highlighted as well.
Note this is different from search, as its not disruptive, since it only adds the highlights.
It’s not essential, but it’s the kind of feature you never knew you needed until you try it : )