Marco Russo and Alberto Ferrari explain when SWITCH is fast and when it’s not so fast:
The SWITCH function in DAX is widely used to define different execution paths depending on the condition of an expression. A very common case is when we want to check the state of a slicer, so that the selection made by the report user directly affects the result of a DAX formula.
Read on for three separate cases and how they can affect the performance of the SWITCH function.