You can use it to drive automation in external apps, without having to leave your inbox. Zapier and other no-code solutions have such integrations, but they are expensive and require access to all your emails. This was something I was not willing to give up, for privacy reasons.
Webhooks are great for producers of events, and I'd argue that it's too cumbersome for them to provide an '/events' endpoint primary because of scaling. With webhooks, they can offload events at their own pace.
For consumers, I agree with most here that Kafka is certainly overkill. We've gotten away with a very simple architecture to have reliable event consumption. We point all webhooks to an (AWS) API Gateway backed by Lambdas. The Lambdas push the events to an SQS queue (FIFO-queue, if it needs some sort of sequence), and we take our time consuming the events through a very generic poll.