A public place is a place of odd and unexpected possibility.
In a busy world where so many things demand attention and there is always a list of things to be done - sometimes a public place is the only place where obligations can be briefly set aside. It's also a place to be a participant with others in a kind of silent, noncommittal way. Often it's a place of watching, reading or waiting. Sometimes it's a place of writing.
Sitting in a public place, you have company, yet you are by yourself. You are with the crowd, but not in it. You can feel lonely there, but you don't have to - with a little imagination, you can also feel your place as a member of our varied human menagerie.
Here, you can quietly observe or discreetly ignore the gaggle of humanity around you. You can chronicle it all - just in your head, or with a camera or a laptop, a drawing pencil and sketchpad, or with a pen and a pocket notebook. Or you can sip your java, ignore your cell phone and revel in this small zone of tranquility.
This, of course, makes a glaring assumption: you have money for coffee, a cell phone and/or any kind of peace. When 11 million people have lost their homes and half the working age population has given up looking for work - that's not a good assumption.
If you are homeless, for sanity's sake you have to carve a private space out of a series of public or shared spaces. I think that's why so many choose to live in a car, (assuming you have one of whatever vintage) - because a car offers the privacy of a door and a lock.
You can't hide out there forever though, and inviting public spaces offer a respite. Of course I have made another assumption: that store owners and citizens aren't complaining and getting non-buyers tossed out for loitering.
My how the mental furniture around here has changed.....
This phone-photo was taken from the second story of the mall, looking down into a sitting area. It was fiddled with digitally in Picnik.