The Input SDK provides a unified interface from which players can discover the mouse and keyboard bindings for any game they wish to play on Google Play Games. At any point during gameplay, a player can summon the Input SDK overlay in a Google Play Games title as seen in this screenshot:
This SDK is required for Google Play Games because Android mobile games are designed around a touchscreen for player input. When developing for PCs, games need to support a mouse and keyboard instead. You should only enable this SDK on Google Play Games.
The Input SDK is a pivotal cognitive component for keeping your players happy and engaged with your game wherever and whenever they want to play. One reason is that Google Play Games allows players to pick up their mobile games on a PC without restarting and replaying the tutorials. Another reason is that the player experience afforded by a mouse and keyboard is different than that of a touchscreen.
For information about integrating the Input SDK, see Get started with the Input SDK.