Photochromic lenses automatically adjust their tint based on UV exposure—darkening in bright sun and lightening when clouds roll in. They're ideal if you ski full days in variable weather and don't want to stop and swap lenses when conditions shift. Think stormy mountain days where it's sunny one run and socked in the next.
The main trade-off is that the transition isn't instant. There's a slight lag as the lens reacts, so you may notice a brief period where the tint hasn't quite caught up to the light around you. Also, in very cold temperatures, photochromic lenses may not darken as fully as you'd like, which can leave you squinting on bright, frigid days.
If you mostly ski in predictable conditions or don't mind carrying a spare lens, interchangeable lenses give you more precise control. But for convenience and adaptability across changing mountain weather, photochromic goggles are a solid one-lens solution—just expect to pay a premium for the technology.