I’ve had these jumper cables for over a year. At least four times I can recall, (and probably more) when someone was already being jumped and all they could get was a click or it barely turned over but wouldn’t go far enough to start, I’ve just put these on instead of the wimpy cables they were using and the engine fired up instantly. Even from a smaller car to a larger one.
If you need to get hundreds of cold-cranking amps over several feet of cable, the voltage drops by the resistance times the current. So even a tiny fraction of an ohm matters when you need that many amps, since you can halve the voltage at the starter. You might barely get enough to the point of connection of the other car, then there are thinner wires to the alternator and a thirsty battery. Your battery and alternator probably provides more than enough but it doesn’t help if it doesn’t get there and instead just warms the jumper cables. Once when I didn’t have these I managed to get a car to barely start by putting a second pair of the thinner cables in parallel.
Forget anything under 6-gauge. 4-gauge can work most of the time. These 2-gauge cables work every time even though they are 20 feet long.