I'll turn it on so that it is making bubbles but not making the surface of the liquid jump( so just a little more than barely open).
I do the same thing. I open the valve slowly until I hear gas leaving the tank and see bubbles, then adjust as necessary to make a gentle bubble stream. The instructions from Williams suggest 50 seconds of air time. I'm not bright enuf to do 50, so I do a minute for 5-5.5 gal of ales. I do 2 minutes for lagers. Having the valve wide open would make a crap ton of foam. I'd also guess holding her wide open would lead to inconsistent results.
Don't know if my ferments are any faster, but lag time from pitch to active fermentation is definately faster. I'm not noticing any fusels. I'd definately say my beer has improved since I started adding O2.