I would put this book, written by Sue Gerhardt, in the overkill category. The point she wants to make is this: pay attention to your baby when she cries.
It is full of interesting information from developmental psychology and neurology, so you know at the biochemical level why it's important to "regulate their emotions" by being at their beck and call for the first 6 months of life. If parents don't do this there are "attachment" issues, which could lead to behavioral and other psychological problems. And there's also the cortisol thing. When you get stressed, a hormone called cortisol is released. It's produced by the adrenal glands, and it gives you energy to make it through the crisis. It also basically tells all of your other body systems, like the immune system, to put things on hold until the crisis is over. Short crises are handled well. Long crises are not handled well by the body. An adult can get sick, for instance, because of an impaired immune system. An infant can have her brain development affected by high levels of cortisol.
But...I found this article in Slate that calls all this into question. Which makes me think, yeah it's good to read some books like this, but it's got to be taken with some hefty granules of salt. If they cite one recent study that "suggests" blah, blah, blah, there's no need to freak out and think you're a horrible parent. This is what I'm telling myself, anyway. I still have no idea what being a parent is like.
Today is D minus 3, by the way...