Which project is "current" when registering a runner?

The help for registering a runner says that --locked means “Lock Runner for current project, defaults to ‘true’ [$REGISTER_LOCKED]”, what does "current mean there? When I’m registering a runner, I’m not working on any GitLab project, but the runner I was about to register should be locked to a particular project.

My guess would be that it is the project that the registration token belongs to.

I had completely forgotten the each project had a registration token for registering a runner for that project. I’ve only set up runners on the instance level.

When you use a registration token for a particular project, the option makes sense and probably means what you say, but when you register a runner for an instance, I still wonder if it does anything.

It makes sense for Project and Group level Runners. I don’t think it has any uses for instance level Runners.