Chuck Adams from the UofA kicked off a series of presentations on the use of space for rituals in the pueblos. Adams is the director of the Homol'ovi project in northern Arizona, and addressed the evolving use of communal space at Homol'ovi over time.
He points out that these "emergent" communities (as labeled by Kate Spielmann) in the Southwest in the 13th century were using Great Kivas and Plazas for the same reason: To integrate the community. Smaller settlements could use a Great Kiva to bring together the entire population at once, while larger communities needed to employ plazas for public sacred activities.
Just a side note: I was unaware that two of the Homol'ovi communities (Homol'ovi I and II) had more than 1100 rooms each.
Darrell Creel from UT-Austin looked further at the relationship between Great Kivas and Plazas, and concludes the plazas were more than shared domestic spaces. At the Swarts ruin, the Great Kiva open onto the plaza. Not such a big deal, but here was the kicker: Of over a thousand total burials at Swarts, the vast majority were inhumations, with only a few cremations... and the cremations were exclusively buried in the plaza, while nearly all inhumations were in or around room blocks.