One follow up question: what do you tend to use your lens for? What subject matter does it surprise you positively and negatively?
Where the skyscape meets the landscape. When start thinking "If only I could go a little wider/higher this would be perfect". When I love what I got but I know there's a still more out of the frame. When the view is BIG, or the view is too close to capture otherwise. When I want to frame a small subject in a big place (get close to them and show everything else around 'em. Interiors when you want to show the whole room without knocking down a wall.
Here are a couple examples, all shot with a D7000.
Two shots of the same waterfall. First at 28mm...
And again taken near the edge of the rock I'm standing on giving you what is essentially the upper-left 1/4 of the previous photo...
This one was taken of a small cabin from about 15 feet away. Could have gotten the cabin and not much else with a 24 or 24mm, and I could not move back more than another 5 feet.
Again, 2 feet back from here I start introducing too much sky or grass into the frame, so I need to consider cropping for a long and thin photo when that's not what I want/need...
There's nowhere I could possibly stand in this building and capture the interior with anything less wide...
And finally, a couple that word have worked just fine with a less wide angle, but became so much more grand when opened up to the 114 degrees of space in front of me.