(a) Allowance of deduction. A loss incurred in a business or in a transaction entered into for profit and arising from the sudden termination of the usefulness in such business or transaction of any nondepreciable property, in a case where such business or transaction is discontinued or where such property is permanently discarded from use therein, shall be allowed as a deduction under section 165(a) for the taxable year in which the loss is actually sustained. For this purpose, the taxable year in which the loss is sustained is not necessarily the taxable year in which the overt act of abandonment, or the loss of title to the property, occurs.