Manual:$wgJobTypesExcludedFromDefaultQueue

Details
Jobs that must be explicitly requested, i.e. aren't run by job runners unless special flags are set.

These can be:
 * Very long-running jobs.
 * Jobs that you would never want to run as part of a page rendering request.
 * Jobs that you want to run on specialized machines ( like transcoding, or a particular machine on your cluster has 'outside' web access you could restrict uploadFromUrl )