Deity has been the basis of human spirituality for thousands of years. Although the deities, and often the ways in which they're worshipped, have changed often, the human need for deity has not. Most Wiccans believe in a two-fold deity: the female aspect and the male aspect. They are referred to as the Goddess and the God. Many Wiccans choose specific deities to fill these roles, others work with a group of deities (calling upon those that are most appropriate for the work being done at the time), and still others do not use any particular deities at all. I am of the last group. I do not feel the need to limit either the goddess or the god energy by conforming it to the archetype of specific deities. However, one benefit of doing so is that you focus the energy you're working with by using an appropriate deity archetype, which adds its own bias to the energy. An example of this would be calling upon Gaia during a ritual to preserve the Earth - Gaia's energy as the Greek Earth Mother would be particularly effective in this case. However, you would not want to call upon her energy during a spell to prevent pregnancy; in this case, it would be counterproductive.
I, personally, do not work with specific deities for one main reason: I do not see the energy within the Universe as divided, such as into male and female. I do, however, recognize this division as a useful tool for the human mind - it is very difficult to consider the energy of the Universe in all of its infinite aspects. Breaking it down into smaller concepts makes it easier to work with. I do, therefore, work with male and female energy, but I could just as easily work with "light" and "dark" energy, or "hard" and "soft" energy, or simply divide it into the four elements - the division itself is trivial in my opinion. Using male and female does provide clear-cut differences, though. We each have a concept of what it decidedly and typically male, and what is female. This makes it easy to differentiate and divide it, and to call upon one versus another, or specific aspects of each.
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