+=item --compact / -c
+
+Compacts the Xapian DBs after indexing. This is recommended
+when using C<--reindex> to avoid running out of disk space
+while indexing multiple inboxes.
+
+While option takes a negligible amount of time compared to
+C<--reindex>, it requires temporarily duplicating the entire
+contents of the Xapian DB.
+
+This switch may be specified twice, in which case compaction
+happens both before and after indexing to minimize the temporal
+footprint of the (re)indexing operation.
+