Many law students purchase this book because they see other students using it or because they are convinced they'll need it. The problem, however, is that this book has more definitions than most law students will need during 1L. By the time you get to your second and third year, you'll probably use the full version of Black's Law Dictionary for drafting legal documents or law journal articles.
It's also not really pocket sized. It's one more book you'll need to fit into your book bag.
In my opinion, there are better and less expensive ways to survive 1L without using this book.
1. Use the law library. I borrowed an older edition of this book from our law library during my first semester. I only referred to it a handful of times. Your library probably also has the full desktop version.
2. Purchase a used version of an older edition of this book. The kinds of legal terms you'll need to look up during 1L generally haven't changed for decades. (Or centuries!)
3. Purchase the Random House Webster's Pocket Legal Dictionary. It's a quarter of the price and MUCH more portable--it actually fits in your pocket. It probably has all of the terms you'll need to look up during 1L. Random House Webster's Pocket Legal Dictionary, Third Edition
4. Use the savings from steps 1-3 to purchase the full version of Black's Law Dictionary. You'll probably still want to use the full version after you graduate. Again, an older edition is probably sufficient.