What is the § ± key for on Mac keyboards?

Some Apple keyboards have a key with § and ± symbols on it. Can somebody tell me what these keys are for, and where I should use them?

I am aware the symbols have mathematical uses, but I assume they must do something important as well to be on the core keyboard. Or are they just the 'Scroll Lock' of the Apple world?

The § is the Section Symbol:

The section sign (§, Unicode U+00A7, HTML entity §), also called the "double S", "sectional symbol" or signum sectionis, is a typographical character used mainly to refer to a particular section of a document, such as a legal code.

The ± is the "plus-minus" sign and you'd use it in text when you're giving a margin of error:

The voltage is 220V ± 5V

As to why they're on the core keyboard, they do have a role in typography and publishing and as a lot of Mac users are in these businesses it probably makes sense to include them.

You say they have to do something important on the core keyboard, but I don't think this is true. Afterall the average user is barely ever going to be using \ or | or [] or {} but these are on the main keyboard. I think it just depends on the use, and it's handier than having to do alt+shift+= for ± Some people will get the use out of them, some will not. It's probably just them symbols as they are the most common to be used out of the alt+[key] symbols (not in my case but could be what Apple are thinking), and they had a key spare.