The purpose of it these days is to bring to attention the rising dangers of nuclear war, rampant climate change, and biological threats. At 90 seconds to midnight, they think shit's pretty fucked. I personally agree with the notion that shit's pretty fucked right now. While their messaging and reporting is important, the way they make their announcement with seemingly no followup could be improved.

If shit gets de-fuckified, they'll typically move the clock back.