A UPF 50+ jersey blocks over 98% of UV radiation, making it the highest sun protection standard in cycling apparel. It's worth seeking out if you do long summer rides, ride at altitude where UV exposure intensifies, have fair or sun-sensitive skin, or spend multiple days touring in the sun. For these scenarios, the protection is a real health benefit, not just a nice-to-have.
The trade-off is that some UPF 50+ constructions can feel slightly less breathable than unrated jerseys, since tighter weaves or UV-blocking treatments reduce airflow. That said, many modern fabrics manage both well, so don't assume you'll be sacrificing comfort.
One important note: even with a UPF 50+ jersey, fabric stretched across your shoulders can let more UV through, and exposed areas like your neck and arms still need sunscreen. Think of UPF 50+ as your baseline defense, not a complete replacement for sun smarts.