Franking credits can only be used if they are attached to...

Franking credits can only be used if they are attached to dividends, such that shareholders receive them when they receive a dividend.
They aren't cashable except in the hands of receiving shareholders, and even then only convert to cash depending on the holder's tax position.
For example, a zero-tax superfund in pension mode would receive a tax refund each year (which can be paid out to the members) comprising all franking credits received.
A corporate shareholder receives negligible benefit, other than fully-franked dividends become tax-free. A foreign shareholder cannot use Australian franking credits.
My private company has millions of franking credits which I may never use, as do many others.
For TBR and RND shareholders, we need to wait until the dominant shareholder, Anton Billis, decides to liquidate the company and pay out the assets in FF cash dividends. Until then, franking credits build up each year due to the companies tax bills, less the small FF dividends we receive.