SSI and marriage

From the Social Security Handbook : http://socialsecurityhop.com/en/handbook/21/2122-marriage

Marriage helps determine whether:
- There is an eligible couple (rather than two eligible individuals);
- The rules for deeming income and resources apply if a spouse is not eligible (see §2167)

Also, from http://www.ssa.gov/policy/docs/issuepapers/ip2003-01.pdf :

(SSI) program, for example, two recipients married to each other receive a benefit that is one-quarter less than if they simply lived together but not as husband and wife.