#memorization

I've been playing chess for a while now, and I've recently started to memorize some opening lines. Not just the basic principles, but actual move sequences. I've got a few friends who play at a similar level, and none of them seem to do this. They just wing it or use a chess engine to analyze during games. Is it normal for people to memorize these lines, or am I just being overzealous? I've sunk a decent amount of time into it, and I'm curious if it's paying off or just a waste...