In very simple language, adding a Cash Balance Plan to supplement an existing 401(k) Plan allows the high income business owners and professionals to contribute substantially more money on a pre-tax basis to their retirement plans.
Example, for 2009, the maximum contribution for a high income business owner to a 401(k) plan is $54,500, assuming they are age 50 or more by 12/31/09. The would normally be accomplished by having a Safe Harbor Cross Tested 401(k) Plan. But, in the right circumstances, you can add a Cash Balance Plan and put away $100,000 to $150,000 (or more) additional for the older business owners without raising the cost of contributions for the support staff significantly.
That's it, in a nutshell - let high income business owners shelter $100,000 to $150,000 more than they can do with a 401(k) Plan alone without normally having to increase contributions for support staff significantly.