They used to say cash is king, but that's definitely not the case any more.
It also used to lubricate many a motor racing transaction and, when I say cash, I literally mean big piles of it. Often in suitcases, sometimes in the proverbial brown envelope. I once had a driver, whose father owned an amusement arcade, bring me a sponsorship payment in £1 coins, which took two mechanics just to lift the boxes.
That's the problem, however, because in days gone by cash became synonymous with undeclared income, which means tax evasion.
This is one reason why governments and central banks promote the convenience, and scrutiny, of digital transactions.