"Checkout SSH keys" vs "SSH Permissions"?

Build Environment
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What’s the difference between setting an SSH key on each of these pages?

–

“Checkout SSH keys” https://circleci.com/gh/<org>/<repo>/edit#checkout – Here are the keys we can currently use to check out your project, submodules, and private GitHub dependencies.

vs

“SSH Permissions” (https://circleci.com/gh/<org>/<repo>/edit#ssh) – Add keys to the build VMs that you need to deploy to your machines. If the hostname field is blank, the key will be used for all hosts.

I assumed that they might be scoped for use only within the “checkout” or “deployment” blocks of the circle.yml, but based on experimentation I don’t think that’s the case.

Thanks!