It provides an extra event onto a competition, ie. skate FS2 and Open Bronze.
It allows skaters who also compete in USFSA to use the same/similar programs without rechoreographing.
The "metal" levels have fewer restrictions on maneuvers, vs. the strict rules in the numbered levels. So, if you have a FS3 element that's good, like a backwards spiral, it can be included without penalty, even if you haven't passed the FS3 test.
It gives skaters who are "stuck" in a level a way to perform/master those higher-level elements while they work towards the FS test, or avoid the problem elements by taking the "metal" level tests instead of the traditional FS tests.
http://www.skateisi.com/site/contentPDF/2010RuleRevisions.pdfPlatinum is the highest Open level and there are no restrictions at all. It's comparable to competing in FS10.
Thanks for the question - it's thought-provoking.