Useful info is useful. I only have one major purchase that I plan to make during one of these sales: Divinity Original Sin 2 :D and am pondering getting the Fallout 4 GOTY version if it comes on a serious sale.

One tip to avoid overspending on games you never get play is to have well-stocked and carefully made wishlists - Steam is great but I also buy a lot of older games on GOG as well ;) - and only buy things on sale from the wishlists. That way you are at least more likely to eventually play those games ;)