One example that comes to mind: we have a networking layer that prioritizes some HTTP requests over others. For example, we seed our cache by firing off requests for the next 30 days, but at a low priority. There was a bug in this layer where request initiation could block the main thread while unrelated work was finishing.

Another example: we used the "HOOKSHOT_TAG" macro to tag objects related to rendering different days in Cue (today, yesterday, tomorrow). This makes the thread activity graph use different colors for time spent on those objects. This helped make obvious a few edge cases where some rendering/processing for a day that was not on screen was done before the day that was.