This option requires that other promotions happen prior to this promotion. This could be useful if you want to enforce a workflow in your promotions such as moving from DEV, to QA, to PROD.

For example, consider a case where promotion DEV is set as the promotion criteria of promotion QA. When the job is built, QA will not be promoted right away as no DEV promotion has run yet. Once the DEV promotion has run QA promotion may be ready to promote, depending on the other promotion criteria you have configured and may execute immediately if all have been met.