Demurrage is exactly the same thing as increasing the money supply. There are no special economic results that will occur under demurrage that will not happen under regular money supply inflation.
Demurrage is simply expressing the amount of bitcoins you have as a fraction of the total supply instead of hard units.
The difference is in debt. Inflating a currency reduces the value of the debt to be paid, but demurrage only reduces the value of the cash you have to pay it off. It seems demurrage could possibly reduce the tendency to put off debt payments.