This is total bullshitAll stems in seedling and veg stage are hollow. In flowering stage the stems are woody not hollow.
Again I'm calling bullshit, many stems are hollow when you get down past the newer growth. Covering those holes is beneficial if you are going to takes some nugs and let others remain. Is there always a problem? Of course not but I have had a few plants wither within days of topping when they have hollow stems. I even take the precaution of treating the lower larger cuts when pruning for air flow.Most stems are not hollow!