I think people (or evidence of people, e.g. roads, buildings etc) can lend tremendous emotional power to landscapes, as well as providing important scale cues. Scale and perspective cues are extremely important in landscape photography, of course, unless one is going for complete abstraction.
The bottom line for me is that I want the viewer to experience a real connection to a landscape. Sometimes one has to find a way to let the viewer experience the scale, if only vicariously, through an actual participant in the scene. I think viewers have a tremendous capacity for sympathetic feelings when they see what others are experiencing, and that line of thinking usually motivates me when I try to include people and evidence of people.