I use this a lot when I need/want to mount a new partition into a directory location that I have been previously been using (i.e. Vinum configuration in FreeBSD). What’s great for me is that it will copy file permissions over properly – and better yet, if it fails partway through you don’t lose any data.
# mkdir newdir
# cd olddir
# tar -cf - . | ( cd newdir && tar -xf - )