Use case: I have a large set of tests, and some of them perform file reads and writes, or operate on extremely large sets of data. When run with my entire test suite, they occasionally cause the test execution to time out, even though the tests pass. They just take a while.
The run and runRemote methods accept a list of white-list labels for tests that should be run, but instead of labeling the majority of my tests as "safe for global runs" I'd rather just label the minority as "long-running" and have them excluded.
Then I could toss a link at the top of the page where I'm showing the test results that would allow me to include/exclude them on-demand without changing any test code.