Simply put, Depth-Of-Field is how much of a photograph is in sharp focus from front to back. Professional photographers understand and use Depth Of Field, while most amateurs don’t. professionals know that they can’t leave this critical element to chance, or to the programmed whims of an automatic camera !
Landscapes Masters, Porter, Weston and Adams always tried to get everything in focus throughout their photographs, to the point of forming Group f/64 in 1932. Part of their original manifesto read : « The name of this Group is derived from a diaphragm number of the photographic lens. It signifies to a large extent the qualities of clearness and definition of the photographic image which is an important element in the work of members of this Group. »
Modern Photography aesthetics accept a wide range of styles, including more impressionistic looks. But in most landscapes images, everything should be in focus unless there’s a specific reason for not doing so – like creating a soft, impressionistic look, or focusing attention on one element.