Inflation encourages investment because if you just sit on your money it gets eaten away by inflation. Once you’re Oprah-rich inflation is the rate at which you’re losing net worth. This is my non-economist understanding.
Inflation affects the value of currency, not assets. Oprah isn’t sitting on billions in cash, presumably. Those billions are invested in assets, which typically inflate at a rate similar to inflation. This is why one of the best hedges against inflation is owning things like real estate and equities. The value is separate from any currency you can denominate it in.
The benefit of mild inflation, to phrase what you wrote a little differently, is that it encourages people to create assets with substantial intrinsic value as a way to dispose of currency. Everyone wants to own as little currency as possible. There are many positive externalities to asset creation.
> Inflation encourages investment because if you just sit on your money it gets eaten away by inflation.
People shouldn't be penalised for saving money.
"Oh, but just invest it!"
With investment comes risk. Why shouldn't people be allowed to save without risk or having their savings melted by lost purchasing power through inflation?
Inflation is a hidden tax and theft of those furthest from the newly "minted" money to benefit those that are closest to the source i.e. banks and large borrowers.
I do wonder if this conventional wisdom is actually true, though. Somewhat relatedly, there was once an idea that if you lower taxes for rich people, they'll invest more, and those tax savings will trickle down to the middle and lower classes and be a boon for them. But we know it doesn't actually work like that.