Apart from expressive power, the standard pooling functions are also widely used thanks to being permutation invariant with respect to the order of the atom representations that are being aggregated. Furthermore, these simple operations are also usually aligned with fundamental physical principles. For example, the total energy, a molecular property, can be obtained as the sum of the atom energies. In general, molecular properties that scale linearly with the number of atoms can be well approximated by fixed functions such as sum or average. However, it is not uncommon for the target property to behave non-linearly or be localised around a small subset of atoms which determine its value. Bioaffinity (the achieved level of inhibition or activation of a drug-like molecule against a protein target) is a property where we can reasonably expect that most of the effect comes from an active group of atoms . In QML, a canonical example of a localised property is the HOMO energy.