I know that. In the case where I started thinking about it, it's a PDOException from Doctrine (no Database present).
What got me thinking is that (in this Silex App), I have a method that checks if there is a connection to the Database. And in a second step, it's checking the available database tables. If one doesn't exist, I need to create it. So I thought about using the try/catch as switch. And that didn't sound valid to me.