It's mainly a test to see if the data can be delivered to the writer quickly enough to avoid 'data starvation' as you can see in this log part:
W 10:17:05 Waiting for buffers to recover... (LBA: 102944)
W 10:17:11 Waiting for hard disk activity to reach threshold level...
It also gives a check that your writer can deal with the commands that is sent to it during the write phase.
As the laser beam is never activated, it can't test that the media will burn without burn fails, generated by bad write quality.
I'll add the above to the guide to avoid future confusion.