I personally think that the way birth is usually done today in North America (hospital, nurse in and out, dad is the main support, doctor comes in at the end), puts a HUGE amount of pressure on the dad, especially the first time dad. My husband was amazing during our first son's birth in the hospital, he definitely stepped up to the challenge, but from my perspective having a doula there would have made things even better, not just for me but for him too.
I think that generally we put too many expectations on dads to be the mom's main support, when he has never been at a birth before (or even if he has), and he is having an emotional reaction (whether acknowledged or not) to what is happening. Having a doula there to support both of you takes a lot of the pressure off, so that dads don't feel helpless (as another post said), and the doula can help direct him if that seems to be required, or just be a knowledgable extra set of hands. Having a doula is such a good idea because she has usually been through birth herself, as well as attended women who are birthing, so she has a wide set of experiences to draw from as well as her training.
My second birth was a home birth with a midwife, and while my husband was already a 'pro' it was so great to have an experienced woman there to help support me as well.
I only read Birthing From Within after the birth of my third child, but I really, really like it. The reason I like it is that you don't actually have to 'know' anything about the birthing process (stages of labour, what will happen etc.) for your body to do it. It's like menstruating or breathing or conceiving and gestating a baby--you don't have to know how it works for it to work. ACCEPTING that it's happening and a natural process that you can trust, and that you can let go and let your instinctual brain take over, are really the most important things.
Our ritual around childbirth, however, is to try to learn about how it happens so we can prepare ourselves. Which I think is very necessary given that most of us birth in the hospital where this information and other evidence-based information about interventions is very important so that we can make informed choices, and even those who birth at home still have a lot of fears transmitted to us from our culture and probably even from our own experiences being born.
However, it's very important to recognize that we don't control birth with our thinking brains, and that knowing about birth and how it happens is not the same as giving in to birth and letting our instinctual brain take over. The best place to birth is a place that feels safe to the instinctual brain, and it's the same for us as all other mammals: warm, dark, private, familiar. Sound like home? The hospital does not feel safe to our instinctual brain, and so those of us who birth there need to be prepared to do more to relax our instinctual brain, and to work harder before birth to confront fears about birth or mothering. Birthing From Within really helps with this process.