It is a buff so you can solo what was formerly a 6-man or small fellowship instance, specifically in Epic Volume I. I am running my 8th alt through Vol I and "Retake Weathertop" Volume I book 2 chapter 5?, for instance, has two choices for completion: Solo, or Group.
I have soloed the last chapter of book 15 on other toons too.
My level 65s enter the instance with 20K morale and beefed up offense and defense.