The fact that you mention getting "relief" partially answers your own question. From a legal standpoint, you do not need to file bankruptcy if you are judgment proof because your creditors won't be able to get anything from you anyway.
However, they can still attempt to collect, which means you will need to possibly show up for judgment debtor examinations to inform the court that your only income is from social security, and that you have no assets, etc.
A lot of this depends on how many different creditors you have. If there's only a few, you can probably just deal with them by letting them know the above facts. But if you have 20 or 30+ then filing bankruptcy is a way to let everyone know in one shot and legally stop them from contacting you and trying to collect.
What it boils down to is how much hassle you can handle. If your thresshold is low, then it might be worth doing a bankruptcy. Otherwise, it's certainly not necessary.
Mark Markus has been practicing exclusively bankruptcy law in California since 1991. He is a Certified Specialist in Bankruptcy Law by the State Bar of California Board of Legal Specialization, AV-Rated by martindale.com, and A+ rated by the Better Business Bureau.