Actually, to understand the importance of reading B. V. Raman's texts perhaps it would be best if I introduced those of you who do not know who he is, to who he was. At present, Raman is the most erudite and influential 20th Century Hindu Jyotishi, who was a magazine editor, lecturer and progressive thinker responsible for informing modern Vedic knowledge with the important fundamentals and advanced principles of classical jyotish. Raman is particularly attributed with introducing classical Vedic principles to Western audiences. Western students, especially, have cherished this great accomplishment, since most of Jyotish was, and still is, to some extent today, preserved and learned through the oral tradition. Raman's highly instructive texts are landmark guides for most serious Vedic students and astrologers. He advised many Indian leaders and other notables, and is attributed with having made a host of accurate predications regarding world events.
The Three Hundred Important Combinations are planetary combinations known as Yogas that most Jyotish students should memorize and know. In fact, knowledge of yogas is perhaps one of the most fundamental interpretative components of reading any Vedic horoscope. The only problem you may face in reading this book is that it is randomly presented. That is, the presentation of the yogas are not organized in a quick reference manner, so this text will almost compel you to learn and memorize the various yogas as you read them--perhaps this was intended (?).
All in all, this is one of the most important texts a Jyotishi student or practitioner could own, and should have in his or her collection.