Heating and cooling with ceilings
High ceilinged rooms feel cooler in the summer. Low ceilinged ones are easier to heat in the winter. For those of us in the "temperate" zone have both scorchers and chill--we generally choose low ceilings and endure the heat.
But maybe there's a low-tech way to have our cake and eat it too.
Suppose the room was built with a high ceiling and with light fixtures that dangle down to or are attached at the usual 8 foot level. In summer the high ceiling keeps you cool with a relative minimum of A/C: ceiling fans alone can keep you cool enough through surprisingly high outdoor temperatures. In late fall, you install a lowered ceiling, with some well-insulated material.
If you use something like boards lifted into place, you have to have mounting brackets installed, and installation can get rather awkward when there's furniture around. In addition, the mounting brackets would be unsightly if permanent, and quite hard to install/remove if they weren't permanent. And you need to have some place to store and easy way to bring the boards into the room. (Perhaps shelving on the walls above the 8 foot height?
Perhaps you could use roll-up partitions that sit in the wall and can be pulled across the air to latch into the far wall. This requires some railguides across the room, which might also be considered unsightly unless they could do dual duty as mounts for track lighting or some such thing. Another problem with roll-up partitions is that they are inevitably thinner than insulated boards would be, and not as good at insulating. Given that there is already insulation between the house and the outdoors this isn't a showstopper.
Supporting the weight of the subceiling gets more awkward as the room size increases. But I don't know of many applications for such a design.
I think this works best for small rooms in relatively small houses: bedrooms, bathrooms, and so on.