Why minimum subscription is needed by the company?

Both of these

The minimum amount that, in the opinion of directors, must be raised to meet the needs of business operations of the company relating to:
 the price of any property purchased, or to be purchased, which has to be met wholly or partly out of the proceeds of issue.
 preliminary expenses payable by the company and any commission payable in connection with the issue of shares.
 the repayment of any money borrowed by the company for the above two matters.
 working capital.
 any other expenditure required for the usual conduct of business operations.