Benefits Behind Gazebo Simulator !

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I assume the question to be: "What values do we add to a robot by building a world in gazebo simulator, like the one here ?"

Answer: If you build a world like that one, a cup on top of a table, in gazebo, you could write and verify a code for PR2 to grab the cup in simulation and later implement the code in the real PR2 without much trouble. For example you could find the proper orientation of the cup at which the robot picks it up easily (here), or the kind of objects (cup, bottle or box) which the robot identifies easily, or the orientation for handing over of objects (see the images here. Or build a world with doors and try to get the robot open the doors in simulation before you do it in real. Not just for PR2, it might give you ideas for other robots too. Etc..Etc! (links are just to give you ideas, not the exact ones)

Or if you were looking for advantages of gazebo simulator in general look here.