If it's more profitable to keep your money under a mattress than to make things, provide services, or provide loans, the economy will tilt toward hoarding cash instead of more productive activities.
This is the classical argument, but I think it's been largely refuted by practice. Instead of hoarding cash inflationary systems motivate hoarding 'things' and then trying to rent them out to everybody. This is arguably even less productive as it's fundamentally socially harmful.
When the value of things naturally declines over time, there's no real motivation to hoard them. And I think hoarding is less harmful than never-ending rent seeking. This entire issue of sidestepping inflation by hoarding+renting is what led to things like the WEF predicting that 'You will own nothing, and be happy.' That's just fundamentally dystopic because it's setting the recreation of feudalism, under a capitalist shell, as a goal. The unstated implication of their prediction is that the super-rich would own everything, and then rent it to you.
