It's the simplest framework I've found to use in the same style as react (databinding, modules, etc) while still allowing you to use the html/css you've probably already written.
This really shines when you want to do something not quite single page appy in your, for instance, bootstrap based site. E.g. a complex web form with some interactivity (autocomplete, add/remove rows, one element affecting another element). This is complex enough to make it a pain to use jquery, but small enough not to want to rewrite the html in a react-compatible way.
That use case seems to be the majority case for me which makes Vue my primary tool these days for web front end.
Good stuff!