Here will be some example use cases you can use googleCloudRunner for.
Since almost any code can be called and passed via Docker images, there are a lot of potential uses.
See the Use Case website menu for some example code.
There are as many use cases as there are different docker images out there which cover pretty much every scenario, for inspiration look around for Docker images that may have cool capabilities. Either make your own or use pre-existing ones.
Some community contributed Cloud Build images are listed here, including hugo, make, and tar.