So I've read quite a bit about cob construction and even after this kind of research, I don't feel equipped to answer this question. What climates or locations make cob a good or bad idea?
One aspect along these lines with which I am comfortable is drainage. You want to be able to keep the 'feet' dry, so impossible drainage -- such as in a swamp, means that cob is a dumb choice.
I suspect that it can't be too hot. What about too cold? What else might I not even be imagining?
I don't think there is a 'too hot' climate limit for cob; like adobe the high thermal mass keeps a cob building cool in a hot climate, and cob, adobe and mud-brick buildings have provided shelter in hot climates since prehistory.
A climate can be too cold; if you live far enough away from the equator there won't be enough sunlight in winter to heat up the cob sufficiently. You could combine your cob structure with straw-bale walls on the north and even the west and east sides to compensate for that.
Other than climate you want to pay attention to your location; you need stable foundations (dig down to solid ground then build up a foundation if needed) and you need to avoid exposed areas (wind erosion, rain blown onto the walls) or valley bottoms (too little sunshine), for example. A swampy area is not necessarily a problem; if you can construct a stable and high enough foundation to keep your cob dry, you can build a cob house.
