If you already own The Witcher 3 on another platform such as Steam, you can grab the game on GOG Galaxy 2.0 for free, too.
If you've only owned the game on Xbox or PS4, this is worth doing if you own a decent enough PC for one simple reason: mods. There's a plethora of graphics, gameplay, and other mods for the game that can really transform the experience, and you can browse some of the ones in our collection for download by clicking here.
While some PC players may find it useful to be able to have a second concurrent copy, such as for having vanilla and modded versions running side by side, most gamers likely won't see a need to do this, however, the GOG version will also be DRM-free, so if that's something you care about, it's worth doing.
You'll need to download GOG Galaxy 2.0 and then connect to the service where you already own the game to claim it. It'll even carry over your achievements and progress, which is nice.
It's a limited time offer, however, and you'll need to act before 12 pm BST on the 23rd of June to take advantage.