I should be surprised were someone to learn the Greek language from scratch using only this book as their grammar tutorial. It is simply too detailed for this purpose.
In conjunction with a smaller, more user-friendly grammar, however, it shines. Once you've learned the basics of a subject, you can use this to supplement and increase your efficacy in the chosen subject. For example, pages 313 to 337 detail the various uses of the genitive case, including possession, partitive, quality, explanation, cause and crime & accountability.
Smyth provides a hefty amount of accidence, although the cases follow Nom, Gen, Dat, Acc, Voc rather than the N V A G D that I would normally expect to encounter. The dual is explicitly catered for, instead of the passing footnotes many of the modern text books seem to espouse.
In summary, I should not recommend buying this book first. Invest in a smaller grammar and familiarise yourself with it before obtaining this weighty tome.