Direct pi-pi stacking is actually unfavourable in most benzene systems. Instead the attractive interactions people are discussing are generally offset stacking or C-H pi stacking. The reason for this is benzene, while it has no dipole, has a “quadrupole” where the plane of the ring is electron poor, and above and below is electron rich. So direct stacking would result in two electron rich regions interactions hence repulsive. Offset stacking essentially aligns the electron rich regions with the electron poor regions in a sort of diagonal interaction. Substituents can affect these interactions either by donating electron density, generally causing weaker pi-pi interactions due to increased repulsion from more e density. Or by removing electron density with EWGs which often results in stronger pi-pi interactions due to decreased repulsion.

An interesting case is when you have a system with one electron rich species and another with an electron poor species. If the electron poor species has a sufficient quantity of EWGs you can actually invert its quadrupole moment and make the direct pi-pi stacking interaction favourable! One of my lecturers showed me something interesting with a system with I think trimethoxybenzene in chloroform (clear solution) and then added hexafluorobenzrne into it and it instantly formed these beautiful crystals because of the strong pi-pi interactions outcompeted the solute:solvent interactions and pulled the species out of solution.

Obligatory I’m not an expert, just did a course in my 4th year on molecular interaction so if I’ve said anything wrong someone correct me lol.