The OBB file is the "soul" of the game. It contains all the heavy data: the textures, the 3D models, the voice acting, the radio stations, and the cutscenes. Without the OBB file, the APK will launch, but you will likely see a black screen or an error message stating that the game data is missing.
Avoid any site offering “GTA Vice City Stories APK + OBB free download.” If you want a safe, legal report on game availability or Android emulation methods for owned copies, I can provide that instead. Let me know how you’d like to proceed. The OBB file is the "soul" of the game