Let me start out by saing that I'm not at all a fan of the machine readable copyright
files - it seems to me there has to be a better way to achieve the use
cases... but!
The use cases are not at all fringe: every company I have worked at since
open source became the dominant source of libraries has had some set of
rules and policies around which licenses to use when, and good data
about that makes decision making easier. As a trivial example GPL 2 only code is not compatible with GPL 3+, so knowing when a dependency changes from GPL 2 to GPL 3+ is crucial for organisations shipping GPL 2 only code [which may not be trivially relicensable, or there might be a practical problem with using GPL3 for that project.
Wearing my HP hat - every time we produce a product containing or depending on open source software we check, in detail, for license compatibility with the product that we're shipping.... Good - accurate and trustable - metadata about what licenses are present is very important to that process. It's equally important to the developers that are choosing what, and how, to build their product - they are often not FLOSS specialists and unaware of the interactions between different licenses and the code they intend to write : does their code need to be open source, or not, does it impact intellectual property, or not ? - This is a large component of why Fossology was born -
http://www.fossology.org/projects/fossology/wiki/About_Us.
-Rob