UI - Logging mouse movement, keyboard events, and other types of attention proxies.

Webhooks and/or Bottlenecks - calling out to either internal or third party classifiers, or more recently even generative models, for personalization based on user tracking data.

And I don't think this is just my unlucky experience. The fine article includes user tracking as one of only three explicitly enumerated reasons for queuing:

> Why? Because users increasingly expect a real-time experience. In use cases like order flows, webhooks, user tracking, etc. users expect to be able to see the new data in the user interface instantly, instead of having to wait for some background batch processing to periodically reload.

Of the explicitly enumerated motivations in the article:

1. "Order flows" - tracking/modification is often one of the higher latency items in order flows ("you might also like" / "what to order next" features).

2. "Webhooks" - often used for tracking/personalization

3. "User tracking" - ...this one is easy :)