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.