I do quite a bit of off-trail hiking in the Sierras, mostly to get to off-trail lakes. If you fish, as I do, lakes off the beaten path usually hold more and larger fish. Some of the best golden trout lakes in the Sierras are off-trail.

Also, camping off-trail affords a degree of solitude I can't often find when camping close to the trail. My favorite aspect of the wilderness experience is solitude, particularly when I'm hiking solo.