Well 1.0 is the only setting that simulates at the same speed as in real life. For all aircraft! 1.0 is the only setting that is realistic.
Using anything but 1.0 is just for training purposes when you cannot keep up with the real speed of things happening.
If you set it to 2.0 for example 1 second in front of your computer is 2 seconds in sim time. Everything is then happening twice as fast as it would in the real world.
Higher figures are just there to save you as a person in front of the screen some time when you fly straight and level and don't want to wait hours to get to your destination.