For the Battletech roleplayer, the Interstellar Players series is the best one in the Catalyst line. In the third book, the idea is that the players are part of a group of freelance and corporate explorers searching for Word of Blake fugitives and looking into what happened to the Clans. As such, knowing what happened in Jihad and the Clan Wars of Reaving would help. Like most Batteltech books, the book is primarily told in character. This unreliable narrative adds to the mystery and the "not all is what it seems" style of the Interstellar Players series.
The book provides an overview of Instellar Expeditions, the corporation behind the explorers, and a chapter on hunting the WoB, including information on the hidden worlds. It then covers the Deep Periphery, including Rimward, Coreward, Anti-Spinward and Spinward. There are a lot of planets and empires covered here, some basic and some intriguing. Some highlights for me were the Society of St. Andreas, a Catholic religious movement, and the Delphi Curse, a virus. There's also a rundown on the competition, which includes governments and the Clans. As a fan of the Clans, I would have liked to have seen more on them.
A person could use this book without the others in the Interstellar Players series, but it's recommended that you pick those up first. This book lacks the basics covered in Interstellar Players 1 and the mind-blowing ideas of Interstellar Players 2. Of the three, though, this offers the most cohesive compaign idea. Someone uninterested in or unfamiliar with the Jihad storyline won't get as much out of this book, but there's still the basic exploration idea.
Buy this if you are a fan of the Instellar Players series. If you are unfamiliar the series, get the first two books as they are five-star additions to any Battletech roleplayer's collection. If you just play the Battletech miniatures game, then you won't need this. However, if you're not roleplaying Battletech, you're really missing out.