RE: abbreviate-file-name on Windows seems incorrect

[Drew Adams]

> > I think that's a mistake. What's gained by that? We already saw
> > what is lost by it.
>
> What is gained is significant performance. What is "lost" is a contrived
> situation of the user's home directory changing from inside Emacs that
> does not really occur in reality.

Can you describe the context and extent of the performance improvement? It
doesn't seem to me to be saving much computation, at a loss of generality,
contrived or otherwise. IOW, what is the use case that this is trying to
support?

I'm not so sure that a change of $HOME inside Emacs, followed by a call to
`abbreviate-file-name' is only contrived. But I admit that I don't have a
specific use case in mind to argue for undoing the optimization. I would
like to understand why the optimization is there, however.