The Canon BG-E16 is the battery grip designed for the Canon EOS 7D Mark II DSLR. All of Canon's Battery Grips are fundamentally similar to each other in design and functionality, and once again, the BG-E16 includes the basics.
DSLRs without a built-in vertical grip (all non-1-Series bodies at this time) have the advantage of being compact and light, but these bodies are not comfortable to shoot with in portrait/vertical orientation - especially for long periods of time. An accessory battery grip solves this problem by adding a vertical grip complete with shutter release and other relevant buttons. And, the grips allow a second battery to be used for double the battery life.
Being easily removable, battery grips allow the DSLR's other advantages to remain available.