The +- metric only counts even-strength goals. So powerplay doesn't count.
Crawford has the best +- in the league, now at +24 after last night.
You can find the odd match where perhaps the +- stat doesn't give the whole story, but there's no arguing with +24 after 21 games. It shows that he's often on the ice when we score and also we don't concede much when he is. For me he's been a great pick up, still young with a physical edge, hopefully he will be with us for many seasons.