Boy did I just open a big ole can of worms. Where to start!? I try to use analogies to help people visualize the subject matter. So let's use Roads in terms of a physical representative for radio signals. Traffic on those roads is the amount of information you can put on that particular roadway.
Interstate highways can carry a lot of traffic. An AM signal comprises the main carrier wave which is modulated with Amplitude and both the upper and lower sidebands. FM has the same characteristics for simplicity. Now where do we build interstate highways? Mostly in the wide open. In terms of radio a strong lightning strike can easily block part of or the entire signal for a time. CB and AM radios can let you listen to lightning strikes hundreds of miles away.
So next is US and State highways smaller roads, less traffic but more importantly don't require much room. This is where we find single side band (SSB). In a SSB transmission only one of the sidebands are used. The carrier and the opposite sidebands is suppressed. SSB is more efficient and slightly less obstructed by things that would make using a full signal all but useless or at least more difficult.
Then there's the county roads that literally go everywhere. Very little traffic can use them at any one time, where I live a tractor waiting at a stop sign is a traffic jam. But these little road snake thire way along winding valleys, and streams, circle farm fields and can deliver you safely to the smallest road we'll call your driveway. This is where Morse Code thrives. In Morse code only the carrier is sent coupled with a modulation tone that is either on, or off, that's it. Not much information. But the information we can send by altering the on/off sequence could fill the entire library of Congress, what's more, because it's so small in bandwidth, it can get through when other roads are blocked. --... ...--