If you tackle the bonus trek up the hill from Illilouette Falls to Panorama Point, this is your reward: views of Half Dome, North and Basket Domes, and in the distance, Mt. Hoffman; a sheer, 2,000-foot dropoff with no guardrails at all; and more stuff you can't see in this photo: a view back to Glacier Point, a view across the eastern end of Yosemite Valley, and a view of lines of hikers making their way up the early stages of the Mist Trail.
Is it worth it? Absolutely. Unless you tell waiters to dip the cherry in vinegar before putting it on your sundae, you always ask for a middle seat when you fly, and you'll cross the street to kick an orphaned puppy - in short, unless you're Eeyore with three bad knees thrown in - this is an essential part of the Illilouette Falls hiking experience.