This question might be off-topic, i don't know where should i ask it.
Google Play's Real Time and Turn-Based multiplayer provide a high-level framework supporting real-time or turn-based multiplayer in your game, respectively. They offer you ways to perform peer-matching and invitation and state updating, as well as providing a pipeline upon which you can build the actual game-specific networking on, if you want.
"Sockets," on the other hand, are a low-level networking concept that allow you to open connections to other devices and transmit arbitrary data back and forth.
Google's services are built on top of sockets, and are thus higher-level and easier to use. If you eschew them in favor of using lower-level sockets APIs, you'll be doing a lot more work yourself to re-implement everything Google's services are providing for you.