As they say, a little knowledge can be a dangerous thing. At the oilfield services company where I work they like to post pictures of the gruesome accidents people have on the job. A recent picture showed a man who had gotten his forarm caught in a piece of machinery, resulting in deep lacerations.
His well meaning buddies had used a piece of cord (tourniquets should be broad and pliant, a belt is good, flat pieces of soft rubber are better) to make a tourniquet on his bicep. He ultimately had his arm amputated below his bicep.
His co-workers saved his life, and I don’t like to second guess people in high pressure, fast moving situations, but based on the picture, I suspect the guy could have kept his right arm had they used rags or bandages to apply direct pressure rather than using a tourniquet. Please note, I am not a doctor or a nurse, but I have had extensive military and wilderness medical training.
Learn how to use a tourniquet properly! Remember, once you put one on, only the hospital can take it off. Using a tourniquet will often result in the loss of the limb below it.