Having just finished discussing this with my better half, who just so happens to work in Business Litigation and IP law, this is very misguided advice, at least here in the USA. Most Federal courts will not even hear a case claiming infringement on unregistered work, in fact, in some cases, the courts have actually made the claimant file to register the copyright before they would even proceed--copyright is Federal and most Fed. courts don't consider unregistered copyrights as being in jurisdiction, and that is the first motion to dismiss that the defendant will make. Each separate motion brought before the court, any of your claims which are contested, any of your evidence which is challenged will cost you money to argue. Registered, there is not much that they can challenge or argue.

She also looked, and can't even find a case, in the history of the America, where any real damages have ever been awarded without a Registered Copyright claim. She did find a few where $1 was awarded, just basically showing that the copyright was probably infringed, but no actual damages successfully proven.

Registration is required to claim statutory damages in US courts as well as to force the thief to pay the legal costs to prosecute their infringement. Typically, the majority of Registered infringement cases are settled out of court because the defendant is essentially going up against the word and statutory laws of the US Government, where they know that they will likely lose big $$$ in both court costs and awards. The main benefit to registration is that you don't have to prove any damages, they are statutory, unregistered you have to prove actual damages, which is pretty tough and very expensive.

You must register your copyright with the Feds if you want to sue.