Thanks for the kind words! QuestDB co-founder here - one example in fintech where you are polling multiple end points simultaneously for market data acquisition. You can think of multiple financial exchanges sending the data, but the latency varies for each venue. This is a great article written by one of our contributors about ingesting data from multiple crypto exchanges at the same time . Many firms in financial services and fintech use QuestDB 
Another would be a manufacturing firm with thousands of sensors sending data to the database continuously, latency and delivery mechanism mean that timestamps often arrive out of order. There is a case study we did with CNC machines manufacturer DATRON .
Tracking moving vehicles (say cars, ships, drones, planes) on a map where the two primary axis are time and space - if you want to see the position of those vehicles in the past, you want to have the timestamps ordered.
Finally you can think of typical devops/monitoring/alerting use cases. Verizon uses QuestDB to monitor metrics for autoscaling decision to their Vespa engine that provides search, recommendation, and personalization to their users . Here you want the series to be ordered by time.