To me using a wide angle lens is not just about getting more or less in the frame, which is what the Tamron link shows you, althouh sometimes that is important if you cant move back any further. Its about presenting a different perspective on a scene.
For example the following four shots were all taken with a 10mm lens equivalent to 16mm on a full frame camera.
However, if you could have got far enough back, these two
Morcambe_Bay.jpg or
Sutton_Park-6283.jpgcould have been taken with say a 24mm, 28 mm or even a 50mm lens and cropped to the letterbox format.
However these two
Birmingham-6303-Edit_copy_4.jpg and
Birmingham-6333-Edit_copy.jpg I have used the change in perspective that a very short lens brings to alter the perspective in the image.
Some people think that a change in focal length changes perspective - it does not. A change in the position of the photographer changes perspective, but sometimes it is the change in focal length that enables the photographer to change is position. I shall post some examples that demonstrate