My Datsun has a "High Performance Tuning Earth Cable". It looks
fabulous.

For looks, worth every penny. For performance, it's a total waste of your hard-earned dollars. It will not increase performance over the stock system.
If you have a good ground/earth, having seven ground cables (as mine does) won't help increase the peformance.
The
stock system has two grounds. One to the engine (the big black cable) and one to the body (the large wire). Just make sure they are not damaged, and that they are securely fastened. If they are loose, remove and carefully inspect for corrosion. Clean thoroughly if possible, replace if neccesary. Some guys have faulty stock earths/ground so install a "Tuning Earth" and it resolves the faulty system. And so legends are born.
Quote:
If you run an earth strap from your head, you can also help to avoid corrosion through reducing electrolysis.
Yes, this is how the Datsun 1200 was designed, it has a earth cable directly to the engine. And one to the body. The head is earthed through the head bolts (10 earth points).