Ideally, by the time you get to retirement, you'll have a nice amount of savings to live on. But even if you manage to retire with a respectable balance in your IRA or 401(k), you might still need Social Security to pull off the lifestyle you're hoping for.Plus, you can't discount the possibility of a prolonged market downturn during retirement. During a period like that, Social Security could become a crucial source of income as you attempt to leave your investments as untouched as possible. If you're marr ...