Plus/minus is a god awful stat and something that should be thrown away...
However, the 38% of all PIT goals against thing is absolutely alarming. Yikes.
The Penguins give up a goal about every 17 and a half minutes when Johnson is on the ice, easily the worst on their team.
For context, that's still not quite as bad as the Jackets worst - Brandon Dubinsky, who is just under 17 minutes per goal against, but Dubinsky has harder deployments than Johnson.
I think the goals stats, for and against, that go into plus/minus are very useful in the context of usage and teammate performance. That and people need to be mindful of how much these numbers can vary from one stretch of games to the next.
Some things are consistent - Dubinsky is bad at it, and his numbers have gotten worse as the season has gone along.
In the last 16 games Dubinsky is on the ice for a goal against about every 16 minutes. Wennberg was among the best but stumbled at the start of this year. Lately he's back to being the best -
there's only 3 goals against with Wennberg on the ice in 16 games, that's over 200 minutes of 5v5 playing time.