Yes there is a physical cost to having hard currency....
but the money is in one's hands...

The benefit of all the various current paperless currency and methods of saving, spending or sending monies is indeed a modern blessing in many ways.
But dumping all hard currencies ...well...

who has control over your money when it is all digital?
who controls the medium of delivery?
or of storage?
or of security?
it isn't you and me.
It will be corporations and government (at best)

And that frightens many many people.

short term, long term, and far into the future...
I see the benefits ...
But I am wary of the true costs