Branching a folder maintains shares between files and subfolders that are self-contained within the branch, but breaks shares to any link outside the new branch.
For example: If $/foo/a.txt, $/foo/bar/a.txt and $/xyz/a.txt are all shared, and $/foo is branched to $/fooBranch, then $/fooBranch/a.txt and $/fooBranch/bar/a.txt are shared in the new branch. They are not shared with the three original links for a.txt. If in the example the $/foo/a.txt was not part of the share in the trunk, then the file would not be shared at all in the branch because there would be no other links within the branch to share with. This works the same way for folder shares that would be self-contained within the new branch. Deleted links should be counted as actual links when determining whether an item should be shared in the branch.