If you have high client demand on a system but resources are scarce, you’re going to end up with a massive backlog. In an event driven architecture, your input queue would swell. The business does not consider all requests equally important; for example delivering password reset emails is far more important than delivering a newsletter.
I’ve written a blog post with a colleague about how we enabled load shedding and prioritization in an event driven architecture using an algorithm that is used in TCP congestion control.