pre-tax is not always a good stuff.  why?

salary you elect to use to pay for Plan benefits is free from income and FICA taxes, i.e. pre-tax. This is a valuable benefit. However, because amounts deferred under the Plan are not counted as wages when determining your Social Security benefit, it is possible that there may be a reduction in your Social Security benefits. If your salary is above the Social Security Taxable Wage Base ($113,700 in 2013) your Social Security benefits probably will not be affected. If your salary is below the Social Security Taxable Wage Base, your Social Security benefits might be reduced. You should consult your own financial or tax advisor to determine the effects of electing to participate in any pre-tax Plan.