Cos the T&Cs say this:
"Unless otherwise stated, you cannot change or cancel your booking once booked or ordered and no refunds or re-credits of Clubcard Vouchers will be given in these circumstances, however unused and in-date Tokens can be returned to us for a points refund."
I want to book tickets for a possible "rainy day"activity when we are on holiday. But if we do not get any "rainy days" they are likely to be unused.