It's just important that they are there. As Pagans, most of us believe that prayer, mediation, magick, concentration etc deal with energies that both outside of our bodies as well as inside our bodies. There is no such thing as an inpenetrable entity. All of us can fall vicitim to the negative vibe. When that happens, our talents are afflicted.
Writers get Writers Bloc.
When these things happen, they do not happen because of bad luck. They happen because we don't do enough to keep ourselves mentally in balance. If we expect to be able to use our minds and our will to create magick and make things happen, then we have to expose ourselves to as little negative energy as possible. Hanging pagan symbols on your wall, or growing herbs in the window is also a wonderful way to celebrate your paganism. The wonderful thing about Wicca is that is not merely a dedicatory religion, but it is highly celebratory.