Subtotals in Apptio offer a great, categorized view of data in report tables. The use of subtotals is encouraged to help present data in a way that is as easy to understand as possible. Subtotals can be very resource intensive on the backing system and should be added to reports with some caution. If the data set being subtotaled is very large it can lead to a large increase in pre-calculation times. It is generally recommended to avoid adding subtotals to tables greater than 10,000 rows.

You can gain some perspective on how much impact a subtotal will have you can add the subtotal to the table you want to use it on and watch to see if the table displays ‘Calculating (x)’.

If this happens then the table is causing a calculation that will take some time to return the result set. If this continues for an extended period of time then the subtotal is likely going to have a significant impact on the total pre-calculation time when published to Staging or Production.
Note:  When testing this, if the calculation takes a very long time and doesn’t complete then it is best to revert your changes when you check -in the document to prevent performance issues in the Development environment.