Comment 1 for bug 1909269

This is one of two per-user quotas, the other being 'key_pairs', where usages are not considered when validating limit create/update. They're always at zero. You can find more information at [1]

[1] https://github.com/openstack/nova/blob/7527fdf6eafe47f0f783e9cdae8b79b76d6ca6b3/nova/quota.py#L178-L182