I'll nominate the "tinkering" at Shoreacres, which was laid out by Tom Doak and implemented in a relatively seamless fashion over a period of maybe three years, as a great example of the benefits of tweaking. It involved tree removal, fairway widening and the removal of rough grass around greenside bunkers and at the entrance to fairway bunkers. They also added a handful of back tees, but the genius of the work, methinks, has little to do with length. It's more about bringing angles into play from the fairway, expanding vistas which brings sun and wind into play and making the course more difficult by removing the rough grass barriers from bunkers.