Not quite sure where he's coming from on that.
The idea of the glide is both to make it easier on the operator, and improve the airflow at the business end.
If you have to put loads of effort into pressing the wand down you're kind of defeating the object of increased operator ease!
Also, by pressing really hard into the carpet you're undermining the benefit that the glide gives you, you're restricting the air flow.
A glide won't get better results than your equipment is capable of, but not using a glide can mean that, at times, your equipment isn't performing at full capacity. Whenever you start to get lock-down your airflow reduces, thus decreasing the amount of moisture and soil that is being removed. The glide helps to minimise this, so increases efficiency.
I find on most carpets, simply the weight of the wand (12 inch 2-jet) is sufficient, I sometimes catch myself extracting one-handed
