I thought it was only sunburn that was dangerous rather than incidental exposure. This has been the advice for years now, has it changed?

Skin damage from UV is cumulative. How careful you have to be depends on your skin type but the general advice is that sun protection should be worn when the UV index is over 3, or if you're spending any extended time in the sun.

"it's only sunburn that's dangerous" stopped being the advice years ago, probably because people (younger dumb me included) were like "I only get sunburn once a year and after that I don't need sunscreen!"