Functions such as COUNT and AVERAGE evaluate a count of cells. You should question whether to evaluate an empty cell by this type of function In practice, it sometimes makes sense to count the number of empty cells. For example, when counting the number of sales reps, the salesrep should be included in the count regardless of whether she sold something. Each no-sale results in an empty cell. There are other situations in which empty cells should not be counted, such as when getting the average of sales over a certain domain. In this case, counting the “no sales” cells would inaccurately decrease the average.
MDX allows for both these scenarios. All numeric functions other than COUNT ignore empty cells. If empty cells need to be included in the count, the consumer can use the COALESCEEMPTY function to force a cell to be treated as a “regular” cell. The COUNT function has an optional argument, INCLUDEEMPTY, that includes empty cells in the count. In the absence of INCLUDEEMPTY, COUNT ignores empty cells.