Improved coverage. Perhaps the technology won't reacher further from the base stations but hopefully operators will put up more masts rather than just updating the ones they have.
That pipe dream aside there's a race to idle arguement. 5G will use more power but if it's fast enough it may use less power overall. Who doesn't like better battery life?
At the moment battery technology is a bigger problem than data speeds for handsets. We need phones that can last at least 24hrs even if you're using them. Of course more efficient cpus and screens would help with that goal too.