For the record, one reason one might use
find some/dir/ instead of
find some/dir is when
some/dir is actually a symlink to a directory and you do want
find to find files in the directory pointed to by that symlink.
But, in that case, there's a better alternative:
find -H some/dir
-H is an option supported by a few POSIX utilities (
chmod...) which tells the utility to follow symlinks passed as arguments (and just those, not to be confused with
-follow which causes
find to follow every symlink, those passed as arguments but also those found during directory traversal).
That's still not functionally equivalent to
find some/dir/ in the case where
some/dir is actually not a directory. In that case,
find some/dir/ would fail with a Not a directory error while
find -H some/dir would list that non-directory file.