OT Anyone know if this is useful or decorative?

I believe this is the SunTrust Plaza parking garage.

There appear to be 6 floors of office space above the parking levels. The vent or grill or lattice-work you see arcing out of the (north?) side is built into the office levels and is 4 floors high.

I would guess that it doesn't have anything to do with being a vent or having an air-flow function.

It might be a purely architectual feature, possibly with an atrium or large open space behind it.

I have no idea what it is either, never seen anything like it. If it's an architectural feature, it sure is ugly.

Is it always in the same position or has he seen it closed, etc? I'd just stop there one day and see if it's accessible and can be figured out. Or ask someone there.

If you drive on down the street a little further and turn and look up, appears to be a reflection in a window behind the "thingy". Tall window behind it is probably an atrium, so I'm thinking the "thingy" is a louvered awning.

Nah. It's a chute for garbage from the rooftop.. They just made it a bit decorative for the outside view :-)

A "window" for fresh air, great on breezy days. There is another one, opposite corner - on the Peachtree Avenue side of the building- near the corner with Baker street, above the bistro area. Designed to look nice, too, not just a window, per se.