If you have an Xbox One or Xbox 360, the Microsoft Xbox Live Gold service is required to play multiplayer games online. Then, you need a Xbox Live Gold, like Xbox Live 12 Month Gold Membership Key or Xbox Live 3 Month Gold Membership Key.
Xbox Live Gold is Microsoft's online gaming subscription service for Xbox One and Xbox 360, that Multiplayer online gaming is required. Whether you're playing a cooperative game with a single friend on the Internet, or playing a competitive multiplayer game with a group of people you do not know online, you need Xbox Live Gold for that.
However, this service is not necessary to play single player games and it is not necessary to play multiplayer games without connection. For example, you do not have to pay to play a split-screen game with two people in the same room on the same console.
The great advantage of Xbox Live Gold is multiplayer access. Xbox Live Gold is worth it if you want to play multiplayer games on your Xbox One.
The other features are considered a bonus. Microsoft offers a wide range of games with Games With Gold and you can access a constant flow of games when you have patience.
In general, Xbox Live Gold certainly seems to be a more valuable service than Microsoft's Xbox Game Pass. It does not offer a discount for buying more time, still requires a paid membership of Xbox Live Gold to play games offline, and gives access to a library of games that includes many free games for Games.