I started this post as a reply to someone asking about landscape lens selection but I decided to make it a separate post as I've seen this question come up before.
When I see these lens selection questions I assume what they are asking is what focal length is best for landscapes, either in general or for a particular location. Of course, there really isn't a "best" lens for landscapes. The best lens is the lens that best captures your vision of the scene that you are standing in front of at that one point in time. Which could be a lens of any focal length.
Having said that let me explain why I love my Ultra Wide Angle lens. While my landscape lens quiver covers 14-600mm, I take a lot of photos in the 14-18mm focal range. If I was forced to choose only one lens to shoot landscapes with the rest of my life it would be my 14-24mm, and that is because of what shooting at 14-18mm does to a scene that is so beneficial and unique to UWA lenses.
When I first started shooting landscapes I thought that the main benefit of a wide angle lense is that it allows you to capture more of the scene. As I became more experienced I learned that while that can absolutely be a benefit, what really makes a wide angle lens sing is the distortion that the bulbous lens creates and what that distortion does to the image.
This distortion causes objects that are close to the lens to look much larger in relation to objects in the distance. This gives the image depth by creating a visual transition (big to small) through the frame. For example, in this image:
Source on Flickr
Those two wildflowers in the foreground are almost as large as the mountain in the background. Our brain automatically processes that "Big to Small" transition by giving the scene depth, which helps the eye to flow through the image.
This lens distortion also causes lines to converge towards the center of the frame. You can use this lens characteristic to help the composition by recognizing that this convergence creates leading lines that point towards your subject, like in this photo:
Call of the Horns on Flickr
The foreground rocks are converging/pointing towards the background mountain, and the cloud streaks are doing the same in the sky. This all helps with the visual flow by directing the eye towards the subject.
I sometimes see questions along the lines of, "What lens should I buy for landscapes" or "What lenses should I take on this trip for landscapes" with replies that say that if you want to go wider than their already existing 24 or 35 mm lens you can save taking/buying a lens wider than that by just taking a pano and stitching in post. This may get you an equivalent field of view of an UWA, but you will not get the benefits I mentioned above. To me, those benefits are far more important than FOV and why having an UWA in your bag is a must for landscape photography.