Sometimes, you're just not going to be able to make it to a polling location on election day. You may be stationed overseas in the military. Or orbiting the planet on the International Space Station. In those cases, early or absentee voting is a lifesaver. Absentee ballots in the U.S. are mailed out to those who request them ahead of elections. Some states require a stated excuse for absentee voting, but others will allow anyone to vote by mail with no excuse. The federal government also offers its own ballots for citizens living overseas or on active military duty.
Other countries handle absentee ballots differently. In Germany, anyone voting in a federal election can mail in an absentee ballot. At one time, an excuse was required, but Germany changed that law in 2008 [source: Wahlrecht]. The Netherlands allows voting by proxy, meaning one person can go to a polling station, cast his or her own vote, and also cast a vote for someone else. In a 2006 election, one in eight votes was a proxy vote [source: CBS.nl]!
Absentee voting is important because it allows people to vote who would otherwise miss the opportunity. But it's also really convenient (no need to leave home), and that convenience poses a new question: How will we be voting in the future? If easy voting is what we're after, we're going to see a whole lot more Internet voting down the road.