You will start from the beginning again if you leave so it's all up to you traffic sucks.
Not good
It IS possible. I personally would NOT recommend it. The logistics would be a deterrent for me.
It is possible but you have to pass the controls again. Depending on the hour, be sure to be back at least 2 hour before your flight. Also, Altanta Airport is not so close to the center of the city, if you will use a taxi or private transportation , take in count you would spend around 80 min in transportation. I think it's better to use the subway
You can leave the secure area, but will need a boarding pass to return. You'll also need to go through security (TSA) again, so leave yourself plenty of time. There's not much in the vicinity of the airport, but the subway (MARTA) can connect you to downtown Atlanta in about 20 minutes.
I suggest You to stay in Airport. It's better.
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