The third scenario is about how you might use OKRs when your agency is expanding, particularly when you're addressing multiple different markets or sectors. Each market or sector may require markedly different things from you, may demand that your teams are shaped differently or are able to act in differing ways. You may be growing substantially and trying to attract top talent to keep up with the differing needs in these areas. You may even be looking at more than one business model running simultaneously in the business.
In short, they need a healthy degree of autonomy if they're going to do their best.