Calling +/- a bad stat is like saying the number 0 is bad... in that they both tell you 'nothing'. More accurate in my estimation, would be to call anyone that attempts to use +/- as the sole or primary evaluation of a player's performance bad. Thee's nothing wrong with the number, it just IS.
I don't think the bolded goes quite far enough.
+/- is a fundamentally flawed metric in regard to player evaluation. Of course, the big problems are:
- Fails to capture qualitative contributions to goals for or against
- Difficult to adjust for team influences
- Prone to arbitrary results due to random timing of line changes
But even if we ignore the big ones, the 4 items below are a
major issue for anyone attempting to use +/- in a meaningful way.
- Arbitrarily punishes players for spending time on the PP
- Arbitrarily rewards players for spending time on the PK
- Arbitrarily rewards players for being on offense while down a goal
- Arbitrarily rewards players for being on defense while up a goal
^ Unlike the first three, this second group creates a
systemic bias against players who are asked to carry the mail offensively for their teams; and a corresponding bias in favor of defensive specialists.
So it's not enough to say that +/- should never be used as the
primary evaluation of performance. It shouldn't even be used as a
secondary factor, or mixed into a formula, or otherwise employed in comparisons -- because the results are known to be flawed, and introduce a systemic bias into whatever larger picture you're trying to paint.