6. Offset to Ownership Dilution

The prevention or reduction of ownership dilution is an argument in favor of buybacks that goes beyond executive compensation.

For example, take the case of a family-controlled company that has issued new shares to investors to finance a growth project. Over the following years, the firm could then gradually repurchase the new investors' shares to ascertain that the family remains in control. 

Alternatively, it could also be that a firm buys back shares to later use them as method of payment in an M&A transaction---or the firm repurchases shares to offset the diluting effect of past stock-financed acquisitions.

The more general point is that firms can use buybacks to "manage" their ownership structure, which can be a valuable instrument in many situations.