You can process the same events in scheduled batches or as a continuous stream. Start with the time the consumer can wait. A payroll export due tomorrow has a different failure budget from a dispatch screen that must show a new job within eight seconds. Streaming adds checkpoints, retained logs, late-event handling, and an always-running processor. Those obligations need a reason.
Throughput and latency are separate. A batch job can process a large volume quickly once it starts, while a streaming job can fall behind despite running continuously. Compare input rate with processing capacity, then reserve room to recover after an outage. Event time also differs from arrival time. An idle phone may upload yesterday's events today, so define when a result is provisional and how corrections reach its consumers.