At a microscopic level water beads up on the wool fibers. Having these beads of water not connected to each other and not next to your skin means you're a lot more comfortable in wool when it gets a little damp. It's perfect for days when there is mist, light sprinkles or intermittent showers. You don't feel too uncomfortable while it's wet and it quickly drys out afterwards. It beats sweating inside a waterproof jacket.

It's also great on days with a wide temperature range. You can wear the same outfit all day while your buds are constantly stopping for wardrobe changes.

Wool is expensive. If you drop $150 on a jersey you might want to think about putting fenders on your bike before you ruin a nice jersey with motor oil, salt, and horse manure.