Form validation, form elements, search... I've seen
far too many sites try to reinvent a browser textarea or edit box, and fail at very basic things because they didn't handle anything they didn't personally think of. (Some common examples: some of the keyboard controls, or correct handling of scrolling when having enough text in the box to scroll, or the interaction between textarea scrolling and
page scrolling...)
"satisfactory" is exactly what browsers tend to provide, with a side order of "no surprises". Designers reinvent browser functionality on a theory of "I don't want satisfactory, I want delightful and unique", and sometimes they succeed, but often they fail. As a user, I very rarely want "unique" when it comes to design.
You don't have to be held back by browsers, and you may well be able to do better, but many people who think they can do better end up doing worse.