Is everything a stream?
Stream > Batch ?
If everything is considered a "stream" -- either finite (as in batch processing) or unbounded -- then the same infrastructure doesn't just unify the batch and speed layers, but batch processing becomes a subset of stream processing. Image: Datanami
Event Time vs. Processing time
Using streams, you can manage time correctly (by using event time and watermarks), so you can group records correctly, based on when an event occurred, and not just artificially, based on when an event was ingested or processed (which is very often wrong). Image: Akidau
By modeling your problem as a streaming problem, you can keep state across boundaries. So two events that arrive in different time intervals but still belong to the same logical group can still be correlated with each other. Image: Tzoumas