Symbols are a Web developer's dream come true; rather than forcing an end-user to download the same information multiple times, symbols allow for an efficient duplication of objects with far less impact on overall file size. Also, by keeping style and location information separate from the symbol, the same piece of artwork can appear very different throughout your document. Lastly, by using symbols within symbols, your coding efficiency is multiplied.
The flexibility that symbols offer developers is tremendous; one piece of art can be used multiple times and in multiple appearances. Symbols, however, aren't the only impressive feature SVG has to offer. The next hour will introduce you to the concept of masking and clipping objects. A technique familiar to most designers, these two methods of selectively revealing artwork can be useful for "cleaning up rough edges."