If it can do it instantly, that would be great. But why does it need to be faster than real-time? You can't capture video any faster. (Though, "real-time" probably needs some sort of framerate qualifier… no doubt 60 fps is harder to encode than 30 fps.)
Unless you're thinking of re-encoding … on a phone?
Yeah, there's always more processing on a video that can be done. Shake/Jitter reduction, histogram normalisation, hipster-like (instagram) filters, etc. (Just imagine a real time instagram filter for video on your phone.)
Edit: Plus it means less power used since the processor doesn't need to be on for as long to process the video (duty throttle / pulse width modulation etc).