I recently read an article about the Special Counsel regulations from Neal Katyal, and how it could be maintained in a scenario where it is stifled. That said, I know that other branches of government (or states depending on jurisdiction) can conduct investigations as well. In addition this question talks about the various ways to conduct an investigation in U.S. government. All of this lead me to wonder...
Why does a Special Counsel (or likewise) even need to exist if there are more defined, and (arguably) less controversial ways to conduct an investigation?