The main difference between virtual devices (emulators/simulators) and real devices is that emulators/simulators are software-driven, faster to provision, and enable parallel testing, but they cannot fully replicate device hardware. Real devices, on the other hand, provide a more accurate test environment, but can be expensive and time-consuming to provision. A combination of both virtual devices and real devices is recommended for a comprehensive mobile app testing strategy, as it allows for a mix of agility and accuracy. Emulators and simulators are ideal for functional testing, UI layout testing, compatibility testing, unit/system testing, and beta testing, while real devices are better suited for hardware dependencies, display testing, replicate issues to match exact model, camera mocking, push notifications, natural gestures, and error monitoring and reporting. In some cases, it may make sense to perform real-device testing at the same time as emulator testing, especially when aiming for a fast release velocity.