This punctuation is often used inappropriately. When properly used, it can allow for an interesting sentence structure:

• A semicolon can be used to enumerate a list within a sentence, especially if the items in the list involve commas. The following items were found in the suitcase in question: one dildo, black; one ibrator, translucent blue; a bottle of KY jelly, half-full; and three pairs of surgical latex gloves, clear.
• A semicolon can also join two complete sentences that are related; a comma wouldn't work in such a situation.