Did you know that bridge experts have bidding methods which differ depending on whether partner has already passed or not?
They use their main bidding system for opening as dealer ("first seat") or to dealer's left ("second seat"). Different criteria are used to judge whether/what to open in third seat. Further criteria are used when in fourth seat.
The book describes the criteria which you should adopt depending on where you sit at the table. Lawrence provides comprehensive logic as to why your thinking should be different; he presents methods to be adopted in each seat; and he provides ample illustrations and tests to make sure you've understood it.
The variations, as described in the book, are very logical and easy to take in. It might sound as though they will make your bidding much more complex, but this is not the case.
If your answer to my question was "No", I would recommend you buy this book. It will almost certainly improve your game.
But beware. The final third of this book is dedicated to extensions of Reverse Drury, and other minutiae. It is a book for strong players. I recommend Paul Mendeleson for intermediates. See my review.