There's the rub.  There are a number of factors that would come in to play.  I guess I'd need a checklist to see if the needle moved far enough over to justify the no-knock.  Violent felony?  Armed?  Criminal history?  History of resistance?  Who else is, or might be, inside? Victims? Kids?  Is it an apartment (shoot-throughs are a concern), a single dwelling, or a trailer in the middle of 10 acres?  Is there another way, or is this the only viable option?  Can we surround and do a "call-out"?  Use OC / gas?  Will it likely be a gunfight regardless?  What do I gain, or risk losing, by using this tactic?  Are we talking about 2 kilos of coke, or 2 armed gangsters?  Coke never shoots at you, in my experience.  Meth lab?  Do I want to risk a spark or flame?
Not saying I'd get it right every time, but if we could eliminate 50% of our mistakes, would that not be a good thing?  Being a Chief, or Sheriff, hopefully one would have years of experience from the street-level up, and so could think about "all the ways this could go wrong", and ask the right questions.
All that being said, I'm glad I don't have to make those decisions.  And I'm not running for Sheriff, so...