Accruals not reversed during year end

Need your help for the below 3 questions..

1.Generally Accruals are auto reversed in the subsequent months. But during Yearend alone, accruals are made in Standard     mode and not in reversal mode. Why?

2.Also, If the expenses are very less than the accruals, how that excess accruals would be treated during year end?

3.What if, Accrual not made in the month, how the profit/loss statement would be ?

Regards,