By definition, high-impact factor journals are widely read. This means that your readership will in general be less specialised and generally less informed on the key open problems in your field. Most likely, they will also be less interested about the exact details of your study, but they will certainly be interested in the implications of your findings both in your own field and in other, related ones.
An interesting blog post on how to vary your writing style when submitting to a journal with a high impact factor. The author, Dr Marialuisa Aliotta, is a Reader in the School of Physics & Astronomy at the University of Edinburgh. She blogs at Academic Life: Resources for aspiring (and established) academics.