In an interview recorded with John Lomax that's included in this collection, he talks about his intent behind making these recordings. While it's hard not to be put off by his use of vernacular common to that era for referring to the subjects of his recordings, the very fact he went to the time and effort to make them is what you need to remember. Most white people at that time wouldn't have considered anything African Americans, especially those in jail, produced worthy of their notice, let alone worth recording for posterity. In his own way, Lomax was also recognizing how America was divided along racial lines and how that resulted in a distinct culture for each race.
These recordings are fascinating listening because not only is the music great to listen to, they give us a glimpse into another era. The idea that African Americans might have had their own distinct culture in the 1930s would not have been something most of white America would have been willing to recognize. The music on these discs not only shows how strong and vital that culture was, it also makes it obvious how much that culture influenced, and continues to influence, American popular culture.