-dit(bf(--size-only)) Normally rsync will not transfer any files that are
-already the same size and have the same modification time-stamp. With the
-bf(--size-only) option, files will not be transferred if they have the same size,
-regardless of timestamp. This is useful when starting to use rsync
-after using another mirroring system which may not preserve timestamps
-exactly.
+dit(bf(--size-only)) This modifies rsync's "quick check" algorithm for
+finding files that need to be transferred, changing it from the default of
+transferring files with either a changed size or a changed last-modified
+time to just looking for files that have changed in size. This is useful
+when starting to use rsync after using another mirroring system which may
+not preserve timestamps exactly.