In California and other mountain areas there is often no campfires or wood burning above 10,000 feet (lack of trees; delicate ecosystem). In a lot of western states it is too dry to burn firewood safely even in a stove like the Sierra Zip Stove.
Yes wood is efficient but not always the right choice and oftern illegal to burn.
In the Sierra wood burning stoves of any kind are not allowed in restricted zones they are considered camp fires.