The article doesn't do a great job at explaining that this isn't always just filtering, sometimes it's aggregation too.
A mobile client may need data points to display a single page that require calling 20 different APIs. Even if every single backend offered options for filtering as efficiently as possible, you may still need an aggregation service to bundle those 20 calls up into a single (or small set) of service calls to save on round-trip time.
A mobile client may need data points to display a single page that require calling 20 different APIs. Even if every single backend offered options for filtering as efficiently as possible, you may still need an aggregation service to bundle those 20 calls up into a single (or small set) of service calls to save on round-trip time.