I feel, this worth one post.
GoG seems in the recent times gives extra discount options aside what appears on their side for those who are subbed to their newsletter.
These discounts are usualy just 5% extra compared to the currently running discounts, or the usualy running discounts, but that's still an extra bonus, and a good way to call attention to certain games you wouldn't consider otherwise.
Also, if you are lucky, and you want that game from the running deal, this will make it extra cheap
At least once they did giveaway too through this method too (some "how this was made" behind the scenes featurette/documentary/extra, still like 10 bucks worth stuff).