Extensions are imporant to give you full support for a given language which essentially turns VSCode from a text editor into an IDE for said language. The rest of it is small modifications, cosmetic changes and convenience.
I think a major selling point of vscode is that it can productively edit anything. Your project happens to include some secondary languages like markdown, yaml or css? No problem. Same for polyglot developers or codebases. This way you never run into the limits of a language-specialised IDE.
I don't do anything that needs or even benefits much from a ton of extensions. I'd expect someone who is would find VS Code amazingly useful (unless they were overwhelmed by the very large number of available extensions).