I have been looking at what lenses I need to get in order to cover a range of different styles of photography. I have seen that 50mm prime is a very popular one, I'm looking for some advise on: how would I use it if I had one? what's the most common use of this prime lens? what's the bennefit vs a std zoom say 18-55 which you can set at 50mm? many thanks for your kind advise.