The bonus for you is great. You get to see where exactly you will work, is it a cube-farm, office, middle of the center of a huge open room with loud fans blowing everywhere around? This is a hugely important part of deciding on a job that many people overlook.
Also, you get to see the breakroom. Is it clean, spacious, stocked with food/drink or not? I've found that the breakroom is a great glimpse into the soul of an employer and a good way to see how you will be treated as an employee. If the breakroom is nothing but a sink with a giant poster stating "DO YOUR DISHES, I AM NOT YOUR MOMMY" that may be a hint that management is less than warm. Trust me on this one, I know.
Lastly, you get face time with the whole company, and can smile, shake hands, and give a positive first impression on everyone. You will stand out more than other applicants because you will appear friendly, which is a job skill that gets more people hired than anything else I know.
Basically, at the point of an interview you've already been selected as being good enough for the job. Now they are just deciding if they "like you" or if you seem to "fit in". This one little question can give you that edge to get the job.