This is one of those hotly debated topics, like carrying a passport or not.
Anyhow ... a letter writer to the WSJ today pointed out that when the power went out in Spain it was no longer possible to tap and pay or to get cash from ATMs. Meaning a lot of people were stuck and unable to pay for taxis or Ubers. Unlike him who had cash.
That's why I am pro-cash, carrying at least $100 worth of the local stuff just so I feel better.