One of the most serious problems is hoarding. Whenever you have a commodity that has a fixed supply against an increasing demand, inevitably hoarding occurs.
The only reason people would hoard money is if the market is in chock. Something has happened like a natural disaster or more commonly some form of government intervention like creating inflation.
In such a scenario the best thing to do is to hoard money until trade slowly picks up again and entrepreneurs can see what the demand actually is. So this is not a problem.
In a stable market you will be getting a higher risk weighted return from your money if you save them then if you hoard them and saving money just means they will end up in capital goods and technologies instead of in consumer goods. Hoarding money for most people that (have filled there desire for emergency cash and aren't Scrooge McDuck) is a terrible value payoff. It is the very last option only resorted to if all savings are very risky and you don't know what you will need in the immediate future...