Why do we have @ in modules builds?

[John D. Hendrickson]

Warner Losh wrote:
> Does anybody recall why we have @ symlink in our module builds?
> I’m constantly working around issues that this creates. Maybe it is time
> to eliminate it?
> 
> So I’ve posted the following review: https://reviews.freebsd.org/D1100
> 
> Warner
> 

don't know.  ideas

could it be to aid directory sorting thus build order ? or for tar(1) 
order? (base world is static order right?)

could it be used by some script for old bang notation or email 
notification ?  ie, uucp ?