The 'Keep Flag' property -- How does it work? Why does it work?

Question

Within my calculation views I had been encountering problems properly aggregating the measures, when certain attributes were excluded from the result set. An SAP consultant recommended setting the attributes' KeepFlag property to True; that resolved the problem, but I'm not sure why.
The help feature within HANA Studio doesn't mention the Keep Flag property. I haven't been able to find much information about this property online, either.
Exception aggregation modeling with Graphical Calc view states:"The Keep flag will always add [the specified] columns in the group by clause even if they are not selected in the query." This is a good start; however, is there any additional documentation regarding this property?

Answer 1

Thanks, Jody. That explanation is helpful. So should Keep Flag be set to True for all of the columns that the user could potentially exclude from the result set? To illustrate: Given the following sample data:
PRODCODE   LOCATION   QUANTITY
12345      A                 1
23456      B                10
34567      C               100
12345      A                 1
If the result set excludes LOCATION, the aggregated results are incorrect; i.e.,
PRODCODE   QUANTITY
12345             1
23456            10
34567           100
The second occurence of 12345 / A / 1 is inexplicably excluded. Setting LOCATION's Keep Flag property to True restores the second occurrence--resulting in the correct quantities; i.e.,
PRODCODE   QUANTITY
12345             2
23456            10
34567           100
Of course, calculation views typically have many more attribute columns. Should the Keep Flag property be set to True for every one of the columns that the user could potentially exclude from the result set?