I just opened up the app I've been working on for the last 6 weeks, which uses Bootstrap, but really a lot of it is customized. So I wondered whether I could just pull out Bootstrap.
And looking through it, there's really not much of Bootstrap left. But then I'm poking around and there's a dialog box with an attached suffix. And that's not something I really want to fiddle with right now, so having one that Just Works is great.
Of course I could poke around on the web and maybe find some purpose-built HTML that does that task. But with Bootstrap I know that there's a wide range of stuff that works across browsers, and I can just throw it in.