The concept of backup is a pretty common one in fiction.  It can occur in various ways be it through a timely intervention to turn the tide at a crucial moment, or it can be the simply through the appearance of reinforcements after the main battle just to help clean up the mess.  One of the interesting things about the Green Lantern Corps is that it is never exactly clear who is going to show up as there are representatives from all across the cosmos representing them, which can mean some interesting characters showing up to save the day (there will be spoilers here).  One of my favourite such moments was during the course of Blackest Day when a few Green Lanterns (primarily Soranik, Kyle, Kilowog and Guy) are struggling to keep Oa in their hands when all of a sudden Mogo shows up.  This is kind of more impressive that Mogo is a planet that has been granted a green power ring (and has other roles for the corps as well.)  Granted I am reading this backwards as I picked up and read the entire Green Lantern Corps series before reading 52 which preceded it, but I was kind of happy to see Mogo show up there as well.  This was not in the same context as he just interposed himself between the disabled starship of Adam Strange and Starfire and provided them a place to land before they got sucked in by the gravitational pull of a star.  It may seem strange, but for some reason whenever I see a planet show up in someone’s aid I always kind of marvel at how cool of a moment it is.