>It's faster for query, but you also risk that the information become corrupted if the Qty and/or Price fields are updated and the total isn't. It also slow down the INSERT/UPDATE.
>
>>I thought that as long as the computed column was deterministic (something like total AS (Qty * Price)) then it would be calculated at INSERT or UPDATE time only and the column could be used as an index and then optimizable...

Nope. There is no such possibility.
That is Computed column. You don't have to do anything for it. It is calculated by SQL Server depending of formula you put.