It also depends on your lens. Most long zooms get soft at their longest setting so I try to avoid it unless I physically cannot get any closer. Also, as others stated, it depends how you want the scene and subject to look. For instance, with a wide angle zoom like say a 16-50mm or so, if you get close to the subject and shoot wide, its going to make the subject look that much more imposing. So if its a big crazy looking tree, or a statue, it will look like its looming over the background. If you shoot the same scene at 50mm the background and forground would have less of a drastic difference of perspective. PLUS you have the DOF issues. I like shooting from a good distance with my long zoom because it typically ALWAYS gives me a nice short DOF on bird shots and what not. If I got closer (without having a really fast expensive zoom ) I would be revealing more and more of the busy background.
On a side note, one of my first lenses was a Tokina 12-24 cause I was told its a must for landscapes. I had not yet learned or understood how to use it in the method listed above when wanting to exaggerate the subject that is very close to the lens. Needless to say, I sold it because I never had trouble getting distant mountains in the frame and figured that was all it was good for. Now I wish I hadn't.