I actually did not take this picture, but it appears to be a main feeder to a service panel. In most cases those big wires should have 200 amps of current potential. That kind of power can cause a lot of problems for the red wire.
Now think of this, when something does go wrong and you need to turn off your flaming overpowered appliance, how do you turn this off? Maybe there is a main before it, but in a lot of panels there isn’t.