[tor-relays] how reliable is the advertised vs consumed bandwidth on tor metrics

[jensm1]

I just stumbled over this
(https://metrics.torproject.org/bandwidth-flags.html) graph at tor
metrics, which shows advertised exit bandwidth to be around 40Gbit/s and
consumed exit bandwidth around 20Gbit/s. This would mean that we have
about twice as much exit bandwidth than we need, which I strongly doubt.
So now I'm curious about what causes this disparity.

Thanks!