Use case: I'm a developer troubleshooting an error on a cluster of web servers, and I want to view the Apache logs from all servers, in chronological order.
The Stackdriver Logging docs only show you how to select instances by their instance ID. Finding each server's ID is a hassle, especially for a large cluster, and it is especially impractical for managed instance groups that auto-scale. This filter allows you to select log entries from an arbitrary group of servers with a partial name match. For example, assume that your servers are Google Compute Engine instances that are named [region]-[zone]-web-[id].