Depends on your experience level. Im USCF 1800+ and opening study is the last thing i work on. Unless your Expert/Master strength, learn the principles behind the openings you play. There is no need to memorize openings 20+ moves deep, unless you just want to sound chess smart.
Understand the principles behind the openings you play
Understand the pawn structure behind the openings you play
So I just got a fancy, big, fat chess openings book. Sounds jolly, doesn't it? The only problem is that I have no idea to what depth I should study it to. Most of the lines in the book go up to 20, 25 moves. Should I really go that in-depth into the book and devote hours and hours on it, or should I just briefly address each line and do other chess stuff with my time?