В чём разница у папок Android/data и Android/obb? Касательно игр - то кеш в одну папку, то в другую - а разница?

В obb храняться зашифрованые данные приложения.

Выдежка из документации:
OBBs contain a filesystem that maybe be encrypted on disk and mounted on-demand from an application. OBBs are a good way of providing large amounts of binary assets without packaging them into APKs as they may be multiple gigabytes in size. However, due to their size, they're most likely stored in a shared storage pool accessible from all programs. The system does not guarantee the security of the OBB file itself: if any program modifies the OBB, there is no guarantee that a read from that OBB will produce the expected output.