Look at the following players statistics:
What do you make of these stats? It says a bit about how you view the game if you float towards the one at the end first and place a lot of emphasis on it - it shows that you expect your players to be defensively responsible - a minus in this area negates the effort they put forth on the ice. If you look at the points and go by that, you might be more of a fan of what people cringingly call the "new NHL," or wide open scoring with a lack of emphasis on defensive responsibility (or smaller goalie pads).
The second guy might just score, but he looks like a defensive liability. The first guy? Not half bad. It shouldn't surprise you to see that the latter of the two is our very own Bradley Boyes, who led the Blues in scoring but also managed to be last on the team in +/-. The former is Alexei Ponikarovsky of the Toronto Maple Leafs, who led his team in +/-.Plus/Minus is an Essential Statistic
Something that is helpful about the +/- stat is that it can tell someone at a glance who is a defensive liability, and who is a defensive godsend. If you see someone with a +33 rating (say, Travis Zajac of the New Jersey Devils), you automatically catch that hey - he might actually know how to backcheck and defend. Maybe he's not turning the puck over, either - perhaps he has some modicum of responsibility in his own zone (or, perhaps he just plays for NJ, who has a fairly high +/- rating overall with a few exceptions). The fact that he was 20-42-62 last season also tells you that he did not rely solely on his own production to bolster that stat. If you have a defenseman who is +29 (Willie Mitchell of the Vancouver Canucks), that's even better - he is actually doing his job and is doing possibly more work defensively than most forwards although he only had 3 goals that season. When you have guys like both of the players mentioned, you know that they will work hard to make sure that the opposition's point total is small - they understand what a two-way game is.
What do you make of players with an abysmal +/-? A low score in this area might be a major red flag. It could be that the player is just generally atrocious (Brendan Witt? Yeah, I'm looking at you and your -34), or perhaps they have no concept of what defensive play is. One way players, such as Boyes, Marc Savard (yes, he had a good season this year at +25, but he is a career -49) Rod Brind'Amour (-23 this year, and his output is dropping off), and Ilya Kovalchuk (-12, but still 43-48-91) are dynamic, fun, and oftentimes get the "cornerstone of your franchise" moniker. Everyone has their jerseys. No one wants someone's jersey because they lead the team in +/-, but if you lead your team in goals, well, that's where it's at. But, these players are defensive liabilities. They are prone to turnovers, lazy play, no concept of backchecking, and a lot of times are the last ones into their defensive zones. When you have a player responsible for 43 goals and he is a -12 despite that output, there's an issue.
What if you're on a really good, tight team and have a poor +/- rating such as Stephane Veilleux, late of the Minnesota Wild(s) and current prisoner of the Tampa Bay Lightning, something is wrong. He was a -17 on a tight, trap playing Wild team. Get ready to see that +/- sink lower on Tampa, who despite the fact that they beefed up the defense, will probably continue to mismanage them and cycle them faster than that guy in your roto-league drops and adds players.
Often useful too is to look at goal/point output and then overall +/-. The Washington Capitals have Alexander Semin and Alexander Ovechkin. Semin leads his team in +/- (and bongo drum playing) with a +25, while scoring 34 goals. Ovie is in the middle of his squad at a +8... but he scored 56 goals. Which is the bigger defensive liability?
One of the best two-way players in the league is Martin Havlat, late of the Chicago Blackhawks. 29-48-77 and a +29. When healthy, he's probably the perfect player to have on your team. Which is shockingly not enough for the 'Hawks, who dumped him in favor of another excellent 2 way star, Marian Hossa. Apparently there is more to the +/- stat... which we will get to in a second.
There's more than meets the eye, here...
An issue that many people don't take into consideration when looking at the +/- of a player is what is expected of him. Is that player a 4th line grinder out there against the top line? Who are their linemates - are they responsible as well, or are they shoved onto a line with an individual with a finger up their nose (or elsewhere)? Who is on D at the time that the goal is scored - would it be the top pairing, or is it the bottom 2? Also important is who is in goal. I'm fairly sure that someone threw a beach ball past Marty Turco once or twice this season when Mike Modano and his -13 were on the ice. There are a lot of intangibles here to look at. What is the make up of the team as a whole? Some people believe that a -16 on a team like the Thrashers is excusable (even though it comes from defenceman Ron Hainsey). Does that make a +13 like Rich Peverley even more impressive? In any case, a -34 like Witt has is inexcusable, even on a team as abysmal as the Islanders were last season.
Please keep in mind, though, that goals scored against you while your team is on the PK do NOT impact a player's +/- stat, so the aged old excuse "But we use him on the PK!" doesn't work. And if he's a PK specialist, why is his +/- so horrible to begin with? Empty net goals do in fact count against a player's plus minus, so that should be mildly taken into consideration as well, although the difference between a player's current stat and the stat without the empty net goals might be extremely small.
More telling than +/- is something called the Corsi Number, which is mathematically evil but probably correct. The corsi is the number of shots directed at the net when a specific player is on the ice. This eliminates the variable of the goaltender, and places more of an onus on the defensive abilities and shot blocking/preventive skills of the squad on the ice. I would explain it further, but the linked website does a fine job.
Anyway, draw your own conclusions from what I've written here. I'm going to go out on a limb and say that basically, when you look at stats, you want defensemen like Rob Scuderi (+23) and not like Jack Johnson (-18). Yay for LA, they have them both. This should be fun. You might want to look more at 2 way forwards, too, when piecing together a hockey team (or fantasy team), but there is no shame in having an offensive powerhouse like Kovalchuk or Ovechkin there either... just make sure that they're backed up by people who know what they're doing defensively. Someone has to score the goals to get these guys' numbers up... Berglund wasn't a +19 just because of himself.