I had a ROTH 401k before I knew not to take taxes first. Invest 1st. 10% off the top for investing first then tax the remainder. It is one way to dump your income down to try and hit the 15% long term capital gain tax bracket >>>> tax is zero then.
However, the contrary argument is you'll qualify for a smaller loan on say a home loan. Also SSI takes your 35 best income years and throws away the rest. These are all the things you have to consider.