1. It binds two sentences more closely than they would be if separated by a full stop/period. It often replaces a conjunction such as and or but. Writers might consider this appropriate where they are trying to indicate a close relationship between two sentences, or a 'run-on' in meaning from one to the next; they might not want the connection to be broken by the abrupt use of a full stop.
2. It is used as a stronger division than a comma to make meaning clear in a sentence where commas are being used for other purposes. A common example of this use is to separate the items of a list when some of the items themselves contain commas.
3. Use a semicolon between closely related independent clauses not joined by a coordinating conjunction: "I went to the pool; I was informed that it was closed due to scheduled maintenance."
4. Use a semicolon between independent clauses linked with a transitional phrase or conjunctive adverb: "I like to eat cows; they don't, however, like to be eaten by me."
5. Use a semicolon between items in a series containing internal punctuation: "There are several Waffle Houses in Atlanta, Georgia; Greenville, South Carolina; Gainesville, Florida; and Mobile, Alabama."
6. A semicolon can be used to separate independent clauses that are joined by coordinating conjunctions when the clauses have internal commas that might lead to misreading: "After the game, I won a red beanie baby, four edible ingots, and a certificate of excellence; but when the storm came, I lost it all in a torrent of sleet, snow, and profanity."