Why is disk queue length an ineffective measure when there is no latency?

Link: https://social.technet.microsoft.com/wiki/contents/articles/3214.sql-server-monitoring-disk-usage.aspx > You should only use the secondary counters for the drive(s) that have > high latency. If the drive has acceptable latency, there is no point > in moving forward. > > Disk counters that you can monitor to determine disk activity are > divided into the following two groups: > > - Primary > - PhysicalDisk: Avg. Disk sec/Write > - PhysicalDisk: Avg. Disk sec/Read > > - Secondary > - PhysicalDisk: Avg. Disk Queue Length > - PhysicalDisk: Disk Bytes/sec > - PhysicalDisk: Disk Transfers/sec Why is disk queue length an ineffective measure when there is no latency?