Question: Mathjax supports automatic equation numbering:  

<http://cdn.mathjax.org/mathjax/latest/test/sample-eqnum.html>

And equation references:  

<http://cdn.mathjax.org/mathjax/latest/test/sample-eqrefs.html>

The extra code to support this seems to be something like:

```
<script type="text/x-mathjax-config;executed=true">
  MathJax.Hub.Config({ TeX: { equationNumbers: {autoNumber: "AMS"} } });
</script>

```

Would this be an useful feature at MSE ?

Answer: 
I'd also like to see this implemented, though it should only be activated on posts that will have been edited since in order to avoid suddenly having labels on everything put in unstarred environments like `align` and `equation`. As [Arthur suggested](https://math.meta.stackexchange.com/questions/11170/support-for-automatic-equation-numbering-and-labeling-of-equations#comment42234_11170) similar to the [now fixed `\\` escaping issue](https://math.meta.stackexchange.com/q/544/163) this could probably be automated in an easy way by appending a star to all the relevant environments.

As a sidenote, [it is possible to tag/label/(eq)ref equations](https://math.stackexchange.com/questions/537284/what-is-an-bmod-n-for-composite-n) (see [source](https://math.stackexchange.com/revisions/8766de10-36dd-4f05-8c2d-f6eae39a55ab/view-source)), although the [preview of blocks containing `\label`s will be broken](https://math.meta.stackexchange.com/questions/11392/mathjax-preview-broken-when-equations-contain-labels)...
I would like this. It's a 1-line add to the MathJax configuration script, and it has [numerous advantages](https://mattermodeling.meta.stackexchange.com/q/120/5).

I see no reason why you would ever want to *not* number an equation: Maybe you're not referring to it later in your answer, but someone *else* might want to be able to say:

> 
> "In Eq. 4 of this SE answer..."
> 
> 
> 

rather than having to say:

> 
> "In the second equation after Eq. 2 and the 4th equation before Eq. 3, for this SE answer, ..."
> 
> 
> 

Simply: I see no reason not to do it.