Another question about Docker Compose. The docs say to run Meltano Docker this way

docker run -v $(pwd):/project -w /project -p 5000:5000 meltano/meltano ui

( I added the "ui" at the end to be explicit even though ui is the deault ) Q1. What is the docker-compose.yaml file for ? I see it springs up a postgres instance called "warehouse_db" Q2. Without the docker-compose, what does the docker run version above use as a warehouse data store ?