a specific node A is currently executing a job that is configured to use 100% of the node's resources.

while this job is executing, to new jobs are queued that are bound to the same node A: one job is a standard build job, one is a clean-up job, which is also configured to use 100% of the node's resources.

now the very first job finishes, and now both the build job and the clean-up job are executed on the node.