Adding elements just because (and, above it all, just for styling purposes) is wrong, of course. But having - or forcing - a tight coupling between structure (DOM) and layout/styling (CSS) is also wrong. IMHO, standards should try to move in the direction of decoupling; they did the opposite with Flexbox.
Anyway, the most present case for me is really Angular, where DOM elements are usually added because they are needed (and actually beneficial, if you like a component-based architecture and DRYness). Angular 1.x deprecated the `replace` option for element directives a few months ago (i.e. your <my-directive> will be in the DOM). Also, AFAIK, it never supported the `replace` behaviour in components (which are always elements). This means that, currently, Angular and Flexbox don't play very well together...
Anyway, the most present case for me is really Angular, where DOM elements are usually added because they are needed (and actually beneficial, if you like a component-based architecture and DRYness). Angular 1.x deprecated the `replace` option for element directives a few months ago (i.e. your <my-directive> will be in the DOM). Also, AFAIK, it never supported the `replace` behaviour in components (which are always elements). This means that, currently, Angular and Flexbox don't play very well together...