Photography can be about a lot of things and when it comes to carrying gear it can be about compromises. How much space do I have for lenses and how much weight am I willing to carry? When it comes to the wide angle end of things you can’t really beat having a really nice lens that captures an expansive view. Often though for reasons of weight it can be easier to just carry a lighter kit lens that maybe goes down to 18mm on APS-c or maybe a better lens that goes to 16mm but if your willing to carry the extra weight of an additional lens there is something special about going all the way to 12mm on APS-c. This would be equivalent to 18mm on a ‘full frame’ camera. The horizontal angle of view of a 12mm lens on APS-c equates to 88.5 degrees while an 18mm lens is 66 degrees this is a signifigant difference illustrated bellow. (Note I am referring to horizontal angle not diagonal, human vision with two eyes is nearly 180 degrees horizontally but a good portion of that is peripheral)
Done well a wide angle image helps to make the viewer feel more like they are right there looking at the scene for themselves. You can back up of course to take in more of the scene but that isn’t always an option as in the illustration image taken from a logging road bridge deck. Another option is to stitch together several images but that can have issues and isn’t suited to anything with motion. So sometimes there really is no substitute for a good wide-angle lens. Personally as I shoot with a Pentax APS-c DSLR I use the smc PENTAX-DA 12-24mmF4ED AL[IF] but there are different options for it and other camera systems. Additionally these images are combed from 4 different cameras (Pentax K10D,K7,K-01,K3) proving my assertion that spending money on a lens is a better long term investment than on a camera.
Here are sample images with this lens all taken at the widest setting of 12mm