When there is a trail, I follow it. It's always easier and often quicker. I never plan for an off-trail route unless I know there is no trail -- then I do my research, use topo maps and plan a route that I download into my handheld.
Just to put this in context, I'm used walking in remote wilderness areas with 10-25 km distances. It's a different situation in different areas. Your situation may be different where you live.
You also have to be sensitive to the land, whether you are in an urban or wilderness area. It's amazing how fast a few people following a route can start erosion or damage vegetation and streambeds, not to mention animal and/or fish habitats.
If you're going to be a low-impact land user, stay on the trails unless you have to go off them.
In similar vein, I think it is irresonsible to place caches in areas where people would have to cross sensitive terrain or bushwhack heavily. Even in areas where there are no trails, there are always more environmentally friendly routes to take -- old creekbeds, rock formations, gravel or scree, etc.
Regards,
Anthony