In this example, "mem.usage host=machine1 region=NW" and "cpu.user host=machine1 region=NW" originate from the same host. They share the set of tags and timestamp (because the collector generated both measurements at the same time, with hundred of other measurements like this). The only difference between two measurements are the metric name (cpu.user vs mem.usage) and value. In situation like this, it's logical to send the values in bulk, without duplicating the tags and timestamp for each value (especially, when we have dozens of values, instead of two). Using the bulk format this example will look like this: