ResultLookup vs. Lookup
With ResultLookup, the dimensions that are defined in the ResultLookup formula need to be in the current drill state. Also, you can filter on only one value.
Because value driver trees only include information about the Account and Time dimensions, ResultLookup formulas often don't show any data in value driver tree nodes.
With Lookup, the dimensions defined in the Lookup formula don't need to be in the current drill state, and you can maintain more than one member in the filter expression.