How exactly does mediahash help?

[Andy]

Hi,

In the doc on mediahash (http://glamkit.org/performance/index.html) it
says "mediahash makes it very easy to test and tweak your settings
without having to laboriously re-allocate media files to different
hosts."

How exactly does it do that? The doc just says that mediahash takes
the filepath string and run it through an md5 hash. But how does that
help testing and tweaking media serving hosts?

Thanks.