The later as the ability to track regressions based on the previous build. Since browser tests jobs have a linear history, we could take advantage of that plugin. In theory, if a test failed in the previous build, that would not cause the job to FAIL (red) but simply be marked UNSTABLE (yellow). I think it will make the life of developers easier when tracking down tests breakages, got the idea following a mail by @Jdlrobson last week.
Have to test what happens exactly :-)