The population by origin report shows all the parts that make up the total. Births, in-migration, and the people already living in the area add to the count. Deaths and out-migration take away from it. Growing up and growing out capture flows between age groups and only matter when an age filter is applied.
The chart stacks positive components above the line and negative ones below it. This gives a full picture of how each part shapes the total in each year.
This page is useful for seeing all the drivers of population at once. Instead of looking at births, deaths, in-migration, and out-migration on separate pages, this report puts them side by side. It shows how large each part is next to the others.