Sorry to sit on the fence but there is no single purpose to photography. It can be used to sell, to provide evidence, to jog the memory and for many other purposes.

The way you take a photo should be determined by its eventual usage. If a clear medical record is required for example there won't be much scope for art, but if you are trying to sell something an attractive or even shocking image may be what is required.

I occasionally use a camera in connection with my work and in that situation, for the most part, clarity is essential as the shots are used as records. When I'm out playing I try to be a tad creative, and look for the aesthetically pleasing.

I do enjoy both of these aspects of photography. On the one hand there is pleasure in a job well done, and on the other there is the occasional image that I want to hang upon the wall.