Well, they can, but the cost will get more volatile... super oversimplified, it's the difference between drinking at home booze you bought at wholesale prices and keeping a running tab with a local bar/pub. You'll be subject to the bar and any price changes they (read: the currency markets) want to make.
but if they run out before they have paid off the money, dont they have to give it back in some way? At least this sounds like it should have more serious consequences than that.
Its very serious to lose important wartime supplies access. I imagine the general populous isn't happy either, with goods becoming more restricted than even the USSR.