The most important thing that any great chef can do is taste their own food while they're cooking. A chef cooking a dish he or she hasn't tasted before would be like an artist presenting a painting that he or she has never looked at before. You have no idea what the final product is going to be like until you've gotten a sense for it yourself.
Maybe the texture is slightly off and you need to add a little more fat into the mix to bring it together. Maybe it's a little too sour so you want to add some more salt in there to cut back on the acidity. You'll never know that something with the components of your dish are a little off unless you try it yourself. And you sure as shit would rather know that something is off while you're still cooking and can make adjustments rather than when you taste the final product for the first time.
So with that in mind...well what gives? Why won't this lady let little Baby Flay taste every single ingredient going into these cookies? If he wants to house an entire stick of butter, let him house that stick of butter. It's called quality control. A quick handful of flour straight to the face? Only way to know for sure that it's still good. This kid has too much damn pride in his craft to serve some underwhelming cookies to his pre-school classmates. He wants every bite to take those little bastards on an experience. Every bite to tell the story of exactly where that cookie came from. A cookie so good it'll make them shit their huggies, and not just like their typical accidents. So let my man taste test. He's earned it.