Not everyone is in the best of health when a conference happens. (Some time, I’ll tell you about the experience of the student who started to suffer from food poisoning while we were on the plane to a conference.)
Organizers, you might consider having a few light, easily moved chairs for people at your poster sessions. NeuroPolarBear twigged to this at Neuroscience, with one of his recommendations:
More chairs throughout the convention center, including the poster floor, but also the hallways. When you see people sitting on the ground all over the place, it's a sign that there's something missing. That thing is chairs.
But at least don’t do this:
ESA wouldn't give her a chair for her poster session this year (really, wtf)
Yes, having chairs in the poster hall does require enough space and a little planning. But some of your attendees will thank you for it.