I just started looking at this and bought some tools to compare the performance of USB-C cables, because I have a box of Micro- and Mini-USB cables that are largely junk and I'm trying to avoid the same happening as my USB-C collection grows. This is only talking about charging efficiency, not data transfer, and not build quality, price or anything else.
I am just starting out with this but I have measured three so far:
One cheap no-name
Apple one that came with my iPhone 15
UGREEN 100W cable
All three of them are 3.3ft, give or take an inch or so.
The short version of the results is:
No-name = 0.240 ohms, Apple = 0.205 ohms, UGREEN = 0.120 ohms
Power loss = current squared x resistance
With my Apple USB-C charger rated 9V 2.2A that means I'm losing this much in the cable:
No-name = 1.14W, Apple = 0.99W, UGREEN = 0.59W
With power in being 9V x 2.2A = 19.8W the percentages lost are
No-name = 5.8%, Apple = 5.1%, UGREEN = 3.0%
At 5V 2.2A the power lost would be the same in Watts, but the power in is lower so the percentage lost is higher.
For an 80W laptop charge, that is presumably 20V 4A. The numbers would theoretically be:
No-name = 3.84W, Apple = 3.27W, UGREEN = 1.92W
With the higher power going in, the percentages are still in the 2-4% range but the issue is the pure power loss numbers. Watts burned = heat generated and nearly 4W in a 3.3ft cable would get hot for sure.
I say theoretically because you wouldn't want to put 4A through the cables that aren't rated for it, but you get my point - buying a good cable does make a difference. And also, what Apple ships with their product isn't necessarily premium.
Of course, another great way to reduce the resistance of a cable is to buy a shorter one... this is often overlooked but if you don't need a 3.3ft cable, such as if you're using a charger that has a cable to the wall and you can use a 6" or 1ft cable from the charger to the device, then that will waste less power.