such as compressing file revisions (to reduce disk space and increase
performance), removing unreachable objects which may have been
created from prior invocations of 'git add', packing refs, pruning
-reflog, rerere metadata or stale working trees.
+reflog, rerere metadata or stale working trees. May also update ancillary
+indexes such as the commit-graph.
Users are encouraged to run this task on a regular basis within
each repository to maintain good disk space utilization and good