Gold is hoarded and traded much like bitcoin, from what I've seen.
Au is indeed useful, but not so much as nearly indicated by its current pricing. There's a _long_ history of human predilection for gold-as-a-magical-substance versus gold-as-an-industrially-useful-element.
Not exclusively, but for the large part.
If you look at historical English prices, prior to the 19th century, the penny was 1/240 a pound, and the farthing ("four-thing" -- one fourth a penny) was 1/960 a pound. Call it 1/1000th.
A labourer's wage might be 20 pound/yr. It's more useful to think of the farthing as roughly equivalent, at least in work-time, to a dollar, and 20 pound as $20,000.
A pound, then, was a lot of money. And even it was (in English currency) silver. Gold were guineas: 1 pound 10 shilling.