I got this book whilst I was working as a gardener, very useful, but it's also excellently useful for reliable detailed information on home herbal use. The second part of the book tells you it's medicinal, commercial and other uses, describes harvest and preparation (and has details such as whether tincture is more effective than distillation of the herb). It has a bonus over some herbalist books which don't give details of what the active components in a plant are, or how to grow them. It also of course comes from a trusted scientific, rather than new age source. I know many new agers may be credible - but the RHS is even more so.
Super book I'd recommend it to anyone with any interest in herbs, even if you don't even intend to grow or use them, just are curious about learning more about the wonderful world we live in.