The dial you're referring to would be an rf gain, basically it raises and lowers the noise floor.
If you want to listen to or for weak signals you can turn up the rf gain, you'll hear more static but you'll also be able to hear weaker stations.
"But it does me no injury for my neighbour to say there are twenty gods, or no god. It neither picks my pocket nor breaks my leg." - Thomas Jefferson, Notes on the State of Virginia, 1782
Arguing with a truck driver is like wrestling with a pig in mud, eventually you realize the pig enjoys it.