A taxpayer is allowed to carry
forward losses up to eight years. But this is allowed only if you file your taxreturn on time. In case you file a late return, you will not be allowed to
carry forward any losses.
If you have paid excess tax, you can only claim it back by Income tax filing. Also, if there is a delay in sending you a refund, the tax department is liable to pay interest on the refund from the day tax refund becomes due. But in case you file the return late, interest will only be paid from the date of filing of tax return, till the refund is paid to you. You will not get any interest for the period of delay.