That link doesn't work for me, so here's the relevant bit:

Rapid Storage: A new Cloud Storage zonal bucket that enables you to colocate your primary storage with your TPUs or GPUs for optimal utilization. It provides up to 20x faster random-read data loading than a Cloud Storage regional bucket.

(Normally we wouldn't allow a post like this which cherry-picks one bit of a larger article, but judging by the community response it's clear that you've put your finger on something important, so thanks! We're always game to suspend the rules when doing so is interesting.)