Do not confuse a custom summary formula in the report with a formula field for an object. They are totally different things and not related at all, although they both have a formula.
The custom summary formula is only available in the Summary, Matrix, and Joined reports. Use a custom summary formula to calculate additional totals based on the numeric fields available in the report or the record count. The same holds true with the bucket field discussed earlier in this chapter. A custom summary formula created in a report will not affect any other places and is not related to other reports.
When you need to get a value from a Lookup or Master-Detail Relationship object, the formula field is the answer; you cannot use the custom summary formula in the report for this purpose. So whenever you need to get a field value from the parent lookup object for any...