Pedantic is the adjective form of pedant
— a person who puts unnecessary stress on minor or trivial points of learning, displaying a scholarship lacking in judgment or sense of proportion. It also refers to a narrow-minded person who insists on exact adherence to an arbitrary set of rules.
In Dr. Jekyll and Mr. Hyde, Richard Enfield tells Mr. Utterson about an incident he witnessed where a man injured a child and then went calmly into a house. Utterson asks Enfield if he was sure that the man used a key to get into the house. Enfield is a bit offended with the doubt. Utterson, however, explains that he already knows the name of the other party involved in the story and wants Enfield to be as exact as possible:
"I think you might have warned me," returned the other, with a touch of sullenness. "But I have been pedantically exact, as you call it. The fellow had a key; and what's more, he has it still. I saw him use it, not a week ago."
So is being pedantic a good thing? It's a matter of perspective: If you're the pedant, then you might pride yourself on your knowledge of minutiae and your ability to follow the rules — no matter how pointless those rules may be. But if you're on the receiving end of a pedant's guidance, then you could end up very frustrated, indeed!