Subject Calculating data

Hi, I have asked this question previously and Robert Martin suggested a possible solution. See 

47630Re: [IBO] Update summary in TableA based on records in TableB

I wanted to know what are the pros and cons of using other options such as Stored Procedures or Calculated fields.
This must be a common problem. I have several tables. I want to sum the field "HOURS" in TableA, add it to the sum of "HOURS" in TableB and put it all in TableC

The tables contain only 200 records each so I could use a loop on each table and calculate this but the user would have to wait.