I typically only rely on the logical parent/child relationship between cells, and containment there is strict even if geometric containment is only approximate. The logical relationship is useful, for example, in providing a compact representation when you have a large collection of cells: https://h3geo.org/docs/highlights/indexing

I'll use the approximate geometric containment mostly just to get a rough idea of where cells are. For example, in the plots of cells covering California in the link above, plotting the "compacted" cells is still visually useful, even if you aren't seeing the exact boundaries of the uncompacted set it represents.

How do you typically leverage exact geometric containment with S2 in your applications? I'm curious because I work on H3 and h3-py (https://uber.github.io/h3-py), and maybe there's something we can build (or it already exists) that would fit your use case.