I haven't progressed very far, but so far it seems that those enticing "Golden chests" yield cards that you use in multiplayer, and in another game!

Does Thronebreaker, which is advertised as a single-player experience, have a lot of this kind of stuff? It really puts me off the game. Why go through the trouble of exploring stuff, if you just get stuff you can't use in the single-player campaign.

(Also, I seems to mostly get "Failed to unlock x" messages when opening those chests.)

Golden chests contain also gold and wood. Thronebreaker is kind of single-player expansion for Gwent, so it's obvious you'll get something for multiplayer.