Calculation groups can apply specific calculations on top of existing DAX measures. For example, calculation groups can implement time intelligence calculations like year-to-date, year-over-year, and currency conversion – or, they can enable the selection of a measure in an existing report through a slicer.
Calculation groups are easy to use; however, achieving the right design for a model with calculation groups can be challenging when you create multiple calculation groups or when you use calculation items in measures. For this reason, we provide best practices to help you avoid any issues. Deviating from these best practices requires a deep understanding of how calculation groups are designed, to ensure the robustness of your model.
You can find more details in these articles about calculation groups in DAX: