Why do we sometimes need to do yarn install and other times we do not?

I notice that sometimes I need to run yarn install for my packages when the GitPod containers spin up, and other times I do not (I can just run yarn start). It doesn’t seem to matter how long the Pod has been down. Seems weird for this to be intermittent behavior.

I can only guess: Maybe prebuilds are enabled in the .gitpod.yaml file? Or it has to do with the yarn configuration. Then it does not have to do with Gitpod.