The conventional wisdom is to keep all cables as short as possible. The contrary theory is espoused by Ron Bauman in the context of his Omega Mikro cables. His experimentation has confirmed, to his ears, that his cables sound best at a length of at least 8 feet. There is some theory behind this, but the real test comes from critical listening. I've spoken with Lloyd Walker, who sells the Omega Mikro cables, and Lloyd says that his own listening tests with different lengths of this cable confirm what the designer says about this particular design. This may be true of other cables, but this is the only specific instance of which I'm aware.
Unless you have a specific recommendation from the manufacturer, keeping all cables as short as practical is a pretty good rule of thumb.