Cooper Brook Falls Lean-To in the 100 mile wilderness is located in a great spot next to a wallfall right on the trail. The falls can really thunder after a heavy rain.
I have never understood why shelters are so often a 1/4 mile or more off the AT. Many old time 2000 milers have told me most shelters 30-40 years ago were located right on the trail with a white blaze painted on the shelter.