In this report, we have attempted to fundamentally address this selective site-substitution and atomic ordering phenomena for the above-mentioned examples. Both the compounds are already established from experimental grounds, but, the fundamental reason behind the titled problem, is still lacking. For example, why Zn in Cu5Zn3Sb2 chooses particularly one Cu-site of Cu6Zn2Sb2? Similar questions can be raised for the InPd2Cu case. Why Cu chooses one Pd site over the other one? Here, we have taken the experimentally established results and addressed the titled problem, either by using the site energy and/or bond energy argument . Mulliken and Löwdin population analysis, the density of states, and crystal orbital Hamilton population analysis of the experimental and hypothetical configurations were performed after geometrical optimization. Overall, the report aims to provide a better understanding of the selective site substitution and atomic ordering observed in these compounds. This could potentially contribute to a deeper understanding of the behaviour of these compounds and their properties.