A street address is required for voter registration for two reasons: to prevent fraud, and to ensure that voters receive the right ballot for the districts that they live in. For voters who do not receive mail at their street addresses, a post office box or alternate address can be provided for the purpose of receiving election related mail, including absentee ballots. Every time you move, it is important to update your voter registration to reflect this, as you want to vote on the appropriate ballot, and you do not want to deal with an address challenge at the polling place.
The prevention of voter fraud is a very important part of the reason why a street address is required for voter registration. The concern is that people could register to vote in areas they don't actually live in, thereby unfairly influencing the vote in these areas. Or, someone could register to vote in multiple towns, thereby being able to vote multiple times, in a gross abuse of the democratic system. When a street address is required for voter registration, it ensures that duplicate voters can be easily identified.
The issue of where someone lives is also important, and it is another one of the reasons a street address is required for voter registration. A change of address could move a voter to a different district, changing the things and people which he or she could vote on. For example, someone in city limits could vote on city ordinances, while someone outside of city limits could not, or someone could move a block and end up under a different city supervisor. This is why it is important to report a change of address, to ensure that you get a say in who is in authority in your area.
Some people feel that because a street address is required for voter registration, the process discriminates against homeless people, members of the military, and people with non-traditional addresses. In fact, the rights of these voters are very clearly protected, although they may want to talk directly to the registrar of voters when filing a voter registration. Someone who does not have a regular address can file a description of his or her “home base,” or use a map to indicate such a space, and in regions with a mailing address requirement, voters can take advantage of free addresses offered by service organizations.
In the event that a voter's street address is challenged, he or she may be asked to bring proof of your address. For renters, a copy of a rental agreement can be an excellent proof, because even if a house does not have a recognized address, the rental agreement should include a description of the home which will satisfy the requirement. For people who are homeless, it can help to bring a member of a homeless advocacy organization to the polling place to help clear up address challenges, especially in areas where there has been a history of voting rights violations against the homeless.