What is the benefit of installing Oracle Grid Infrastructure software for a stand-alone database?

The Oracle Grid Infrastructure for a standalone server is the Oracle software that provides system support for an Oracle database including volume management, file system, and automatic restart capabilities. If you plan to use Oracle Restart or Oracle Automatic Storage Management (Oracle ASM), then you must install Oracle Grid Infrastructure before you install and create the database

Oracle Grid Infrastructure is a separate part of Oracle software beginning from version11g, used by ASM technology. If you want to use ASM you should install this software.