All mineral grinding mills suffer high wear rates of their internal components. All cylindrical tumbling mills (AG, SAG, Ball and Rod Mills) feature cylindrical structural shells, protected from abrasion by removable, replaceable mill liners. Every tonne of mineral ore must be processed through the grinding mills. When the grinding circuit is stopped for necessary maintenance, the cash flow of the entire mine site effectively ceases. 

John Russell saw a link between mill liner life and at the end of the life precipitated a shut down and changing those liners dictated the length of the shut-down. A critical path element. So there was a weird link between concentrator availability and pivoting around the mill liners. Not only that the amount of the year the concentrator actually ran defined how much the mine site could produce.

So there is a direct link and it has never changed between liner life and liner exchange rate and whole site profitability.

Mill relining is the most specialised maintenance task in a mineral concentrator. 

Almost invariably the AG, SAG and Ball mill liner lives dictate the shut-down dates of the concentrator. The replacement of the mill liners determines the length of each concentrator shut-down.

In other words, the liner lives and their replacement, define the time available for mineral processing. For every hour that the concentrator is shut-down due to liner exchange (Grinding Mill Relining) the mine site asset loses $50K to $500K per hour of revenue, depending on the mine head grade, through-put and commodity prices.