But you can make guarantees to the critical jobs (up to the total size of the machine) and then let batch jobs (with less time-sensitive requirements) run best-

But you can make guarantees to the critical jobs (up to the total size of the machine) and then let batch jobs (with less time-sensitive requirements) run best-effort in the slack. In the event that there ends up being no best-effort resources available on a machine for a significant period of time (because all the user-facing jobs are busy and using their guaranteed resources) Borg will shift the starving batch jobs to other machines that aren't so busy.