As you know, an expense arises when the obligation to transfer economic benefits arises, not when the expenditure actually incurred. That’s called accrual based accounting and as such it’s important to understand all conditions of certain agreements and transactions. It’s crucial to see those moments the obligation actually arises. 

However, sometimes those expenses are spread over periods, or we just know we have to pay up some amount in future, but the conditions are not clear or the time the payment needs to be made is still not sure and so on. This is where you know for sure that you have to pay something and hence you reflect a provision, an estimation of what you will owe, on your statements. Now, with provisions being the topic, you make a following entry (one onto the balance sheet and another on the income statement):

D Expense account

C Provision account

This entry is to say “I know I will encounter an expense some time in the future and I’ve already provided for it to reflect the liability”.

Now the time comes to release the provision. As it happens, those releases should always be included in the same line item as the original income statement the charge was recognized on. What you’ll do is an opposite entry:

D Provision account

C Expense account

Why it’s done is to ensure that line items reflect the true cost of particular expense groups or functions over time.