You are looking for resistance rather than "impedance". Rb has been used with classical bipolar OPs to cancel the addional offset caused by input bias current. As already mentioned "input balancing" could mean a lot of different things, I won't use the term here. Rb = Ri||Rf is the right value. In case, I would talk about source resistance balancing.
The resistor is only meaningful for OPs with |Ib| << |Ios|, that's only the case for bipolar OPs without bias current compensation.