I do it. 2 out of the 5 machines I've owned have a knot button.
I had a 2086 for a while and it bugged me that it didn't have a knot button.
I, personally, think it makes a difference.
On my Star 5, hitting the shift button on a pull increases the tension 5lbs.
Blade 98 18x20 x3 - Babolat VS Team 17g @ 50lbs M's/Signum Pro Poly Plasma 17g @ 46lbs X's (5% pre stretch)-USRSA Certified Stringer-Babolat Star 5