It can be.
The vacuum gauge is a tool, and it definately has a purpose.
However, in virtually all cases, the highest vacuum will be obtained when the throttle plate(s) is(are) closed; as vacuum is measured below the plate(s). Depending on the design of the idle/off idle circuits of the specific carburetor in question; the highest vacuum setting may lead to a hesitation in the transition from the idle to the main circuit(s).
Jon.
