Calculate views aggregations after the query.
Has additional grouping/aggregation features vs core.
Can do grouping functions, or column aggregation in header/footer.
Some things work well, but there are some major issues.
There seems to be some interest, but not a lot of development activity.
Aggregation in views can get pretty complicated. The API is very powerful, but the UI is limited so it's easy to run into confusing blockers.
MR36 in View on Drupal.org #3482129Crashes with Drupal\views_aggregator\Plugin\views\style\Table::setAggregatedGroupValues(): Argument #3 ($group_aggregation_results) must be of type int, string given Status: Reviewed & tested by the community is pretty important.
Submodule views_aggregator_more_functions has sequence number, range diff, and percentage.