Calculation groups
A calculation group is an element of the Tabular Model that can replace a measure expression with the DAX formula of a calculation item.
DAX Optimizer currently does not evaluate calculation items and calculation groups in analyzing the performance of DAX measures.
As a workaround, create a measure that expands the DAX expression of a calculation item applied to another expensive measure so you can figure out the cost of the calculation item by evaluating the difference between the original and the modified measure. Read more in Analyzing calculation groups.
More about calculation groups: