I found another nice feature that is missing from metacity, but
available in mutter. Mutter supports draggable invisible borders
around windows, which makes it easier to resize them. It's especially
useful for themes, which has 1px borders, e.g. Adwaita. You can see
the
relevant bugzilla task for mutter here:
https://bugzilla.gnome.org/show_bug.cgi?id=644930