Litmus tests are for those with either little or no skill in creating OC's, too insecure in their writing and character creation, or for those who want a laugh on how high or low their character will score. All anyone has to do when creating characters is read one of the numerous creating-character books out there, or learn from their mistakes.
Maybe the litmus test can be a guideline on what to avoid with OCs, but I never bother with them. I did one or two for fun and got a low score, but even if my score was high, that wouldn't change how I had the character. The Sue is in the writing, not the traits.
Took three years to be where I'm at now, and none of those skills I gleaned from the litmus test.