I read on e-readers a lot and I've been known to long press a word on the page of a real book to get a definition. Yeah... Muscle memory is a hell of a thing.
I also read some things in the languages I'm trying to learn, and this feature is essential for translating words I don't know yet.
Plus, the backlight (adjusted for warmth so as not to keep me up) lets me read in bed with the light off and I don't have to get up to turn it off when I'm done.
I was very pro only real books for a while, and still am a fan of a real book, but the quality of life features of e-readers eventually sold me. Especially because night is one of the few times I can read.
Sometimes I look for a search button on paper book. I read most of the books in electronic format nowadays, so reading paper book is a rarity. In fact I often buy electronic format for a book that I already have in paper form from “older times”. Reading e-ink is much easier, especially in the dark of night, and it is less heavy too.