Or I'm doing something silly but my theme  has multiple places where I want to show a flash message.

I'm not sure how I would handle that with only a flash bag that has success, error and warning. How could I know then where to show them? Personally I set the key to 'message_info'. And then in my layout i check for message_info flashes on the messenger pages. So then I can show them in the right place and I know they are 'message flashes' not other ones...

But I agree for most it would be overkill... or again maybe I do something wrong