The only time I’ve ever seen it is in cases like Google±formatting, where it’s a mistake. How can it be turned off?
AI-generated summary
A discussion is taking place about the automatic formatting of +- in Discourse. notriddle wants to turn off this feature, citing its misuse in certain cases. mcdanlj thinks it’s useful for science and math content. sam suggests disabling enable markdown typographer to turn off the feature, but notes that the notation can be handy for certain expressions, such as Removing this feature will take 1 week +-90%. Stephen is undecided, but thinks it’s more common to use +/- in some regions, and suggests keeping the conversion and educating users on alternative notations for rare edge cases.
For science or math content, it makes sense. I can edit my post… 
You would have to disable all of enable markdown typographer I agree it is somewhat odd, but not sure if we should ship our own defaults for typographer, this is the first I ever heard of this +- problem, I think notation wise this can be handy for stuff such as:
Removing this feature will take 1 week ±90%
I’m on the fence on this one. For example here in the UK many keyboards including my own has the ±, so we don’t need the conversion.
It should probably come down to whichever is the more common notation. The instance in the Google+ Exporter topic was probably the first time I’ve seen it arise here, it’s going to be even less common after April.
It probably makes more sense to keep the conversion and educate users on the alternative for the rare edge cases where +- is intentional.