This is a brief (104 pages) treatise on liturgy.  It's considered by many to be the liturgical equivalent of Strunk & White's famous Elements of Style.  Whether you consider Kavanagh's book to be that influential and helpful probably depends a great deal on your preconceived notions about liturgy.

Admittedly, this book would be of primary interest to pastors and others engaged in regular leading of worship.  That's the focus of the book.  How you do it and why you do it.  Not in the technical sense of the word, but in the more aesthetic, artistic sense.  Kavanagh writes from a very conservative liturgical stance (as well as a Roman Catholic one).  Not necessarily high church in terms of complicated and intricate liturgies, but from the perspective that he takes liturgy seriously as something that does things to us, rather than something we simply have the freedom to do things to or with.  As such, pastors and leaders in liturgical denominations will probably find this most helpful.

However, I'll be a nerd and argue that this book has a broader audience, potentially.  It isn't just those who lead liturgy who ought to understand and respect it.  Those who participate in liturgy should understand and respect it as well.  And while the respect is traditionally there (though less so as time progresses), the understanding isn't always.  Pastors and liturgical leaders have the benefit of special training and education to help them appreciate and understand what they're doing.  It doesn't always stick, but at least they've been exposed to it.  Most folks in the pew have not.  They participate in liturgy (or are subjected to it) every week in worship but aren't necessarily formally educated in what they're doing or why.  I think that's unfortunate.

If more folks understood the nature of liturgy and public worship, it might better inform our discussions of it and our decisions to modify it.  Tragically, it's often more fun to complain than it is to really think through what we're doing and why and potentially change our opinions (and eventually our tastes) accordingly.  

Almost a year ago I attempted to engage in a discussion on Facebook with an acquaintance from a different theological tradition on the issue of worship.  They were lamenting about how terrible worship was in any number of their denominational congregations in the area.  I asked them what they understood worship to be, and more importantly, what their denomination understood it to be.  In other words, I can complain about something I don't care for.  But what is the basis for my not caring for it?  Would I care for it more if I understood what it was and why it's there?  Maybe.  Maybe not.  But it would give me a basis from which to critique my own preferences.  

As is often the case, the Facebook conversation eventually went nowhere, which is a shame.  While it was clear that people have strong opinions, it was also clear that most of the folks involved in the discussion didn't really want to go to the effort of exploring the matter more deeply.  They were most concerned with their immediate tastes and preferences.  But if that's all we have to go by, then it's a pretty relativistic field we're playing on.  Who says my tastes and preferences should dictate?  Why not someone else's - even if that someone else died 400 years ago?

So, this book can be helpful.  He's not advocating so much about what should be done, but he discusses some of what is done and why.  And more importantly, he offers a pretty sane voice in terms of how leaders ought to approach worship in the sense of not only what they do or don't do, but how they do it or not.  

If you're nerdy, this might appeal to you.  If you aren't, then read something else - or get this as a sleeping aid.