a!localVariables() which statement is true

What are you trying to find out exaclty?

Both are potentially true depending on the context.  The a!localVariables() call can be evaluated as empty (i.e. not actually containing any variables) if needed, though there's almost never any benefit to doing that, other than when you put it in as a placeholder when first starting a rule/form (like when you know some variables WILL need to be added, you just don't know WHAT at first).  And having local variables CAN increase the number of queries executed if structured poorly, or if extra variables are created that don't end up being needed - but the NORMAL use case is that having variables will DECREASE queries executed, since it reduces instances where the same logic needs to be run over and over again, for instance.

What are you trying to find out exaclty?

Both are potentially true depending on the context.  The a!localVariables() call can be evaluated as empty (i.e. not actually containing any variables) if needed, though there's almost never any benefit to doing that, other than when you put it in as a placeholder when first starting a rule/form (like when you know some variables WILL need to be added, you just don't know WHAT at first).  And having local variables CAN increase the number of queries executed if structured poorly, or if extra variables are created that don't end up being needed - but the NORMAL use case is that having variables will DECREASE queries executed, since it reduces instances where the same logic needs to be run over and over again, for instance.