To Insulate or not to insulate ?

After lots and lots and lots of reading.... I think my daughter and I have decided on an overall shape and style of tear.
The one item that still vexes me is whether or not to build with insulated floor and walls.
Another way to phrase this question is whether or not to build with a framed wall and floor verses using nothing but one or two sheets of plywood with cutouts.
The insulated option that suits me would be a sandwich with as little framing on the inside as necessary to keep the weight down.
I would also use as thin of panels as possible, again for weight.
So... what has driven folks' decision to build with 1/2" to 3/4" of insulation in the walls?
I'm not so vexed about the floor, since it just makes sense to me to frame the floor.
The ceiling is a non-issue to insulate, because I would build it framed no matter what.
Thanks up front for your shared opinions.
The one item that still vexes me is whether or not to build with insulated floor and walls.
Another way to phrase this question is whether or not to build with a framed wall and floor verses using nothing but one or two sheets of plywood with cutouts.
The insulated option that suits me would be a sandwich with as little framing on the inside as necessary to keep the weight down.
I would also use as thin of panels as possible, again for weight.
So... what has driven folks' decision to build with 1/2" to 3/4" of insulation in the walls?
I'm not so vexed about the floor, since it just makes sense to me to frame the floor.
The ceiling is a non-issue to insulate, because I would build it framed no matter what.
Thanks up front for your shared opinions.