I found this book to be essential to my successful studies at Fuller Theological Seminary where I earned my MDiv. In Koine (Biblical Greek), as in all other languages, there are irregular forms of verbs, participles, nouns, etc. Working with the unusual forms and working them back to the standard entry form for the more in-depth lexicons is more than a little time consuming. With Moulton's Analytical Greek Lexicon, one can find the specific word (spelling) and learn how it is parsed out. From that, one is able to get the root which is then useful in other lexicons and studies - be it BADG, Kittle, etc. If all one needs is a quick definition of the Greek word, it is provided for the user.
I completed my Greek studies at Fuller almost 30 years ago. I've forgotten a lot over that time. Moulton's has become even more important to me. Even with such online helps as interlinears keyed to Strong's and other Biblical Greek helps - this one book retains its place as the first or second most important tool in my library.