The spirit of Indian Defenses is based on flexibility and harmony.
Most of the lines are positional, not tactical in character.
While playing Black, you have to accept that occasionally you will not equalize, or get surprised or out-prepared.
Learning the material from this book should sharply limit the extent of such instances, thus improving your overall results.
Finally, we have an important piece of advice: remember about color strategy!
The Bogo-Indian is mainly based on dark-squared control, while the Nimzo-Indian does so on the light squares. In case you forget what to do, this may prove a very useful guideline when choosing a move.