Absentee ballots are increasingly being used throughout the United States. They are especially popular in the West Coast; elections are entirely absentee-ballot in Oregon and Washington, for instance.
The general reasoning behind absentee ballots are that they increase voter turn-out. The theory goes that voters too busy on election day can vote before the election. Absentee ballots make voting simpler, people say. If it is true that absentee ballots increase voter turn-out, then this would be a substantial advantage.
There is another great advantage to absentee ballots, however. Absentee ballots enable voters to make informed decisions, especially about local elections and measures which nobody has heard of.