Donna Farhi is a soft spoken, yet strong woman. (See post about strength.) I'm a sucker for a New Zealand accent, and she's got one! It's a pleasure to work with Ms Farhi in person. However, there's a lot to be said about reading any of her many books.
Pranayama is definitely a disciplined activity offering great rewards when practiced with dedicated awareness and honesty. However, the over-zealous (yes, I admit I can fall into this category) may perform advanced pranayama techniques before they're ready. This is where Farhi's book comes into play.
Donna doesn't talk about pranayama. A matter of fact it's only referred to twice. Once in a listing for supplies to aid in breathing exercises, and the other time on page 9. She says,
"On a deeper level, highly controlled breathing practices such as those employed in yogic pranayama can backfire because they can act to repress the underlying psychological fears and issues that are driving poor breathing habits in the first place."
So as useful as pranayama can be, it is imperative to first understand your breath and explore more organically. By that, I mean to work with less control and more softness prior to a stricter discipline, such as pranayama. That way, you'll know if you are pushing too hard. Learn what relaxed and full breathing is, so you know when you are deviating from it. Make sense?
If you've practiced Yoga, you'll notice that this book doesn't read like other Yoga books. The exercises are not necessarily "Yoga moves." Regardless of whether-or-not Yoga is a part of your life, this book is invaluable in learning how to breath.