Why do companies use share repurchase programs?

I. To increase share price over the long term by increasing a continuing shareholder's portion of the future cash flows.
II. To optimize the company's capital structure.
III. To return capital to shareholders in a more tax efficient manner than cash dividend payouts.
IV. To offset the dilutive impact of other share issuance programs such as stock option programs.
V. To redeploy excess cash flow.