the most obvious case is that people don't have a bank account or are 'underbanked' in the US that amounts to about a quarter of the population[1]. I think covid has shown what a mess it is to get everyone their relief money. If everyone had a digital account with the FED it'd literally be a few clicks of a button.

[1]https://www.cnbc.com/2019/03/08/25percent-of-us-households-a...