Back-collecting is also quite useful for small nations that are receiving a lot of foreign aid, for example, tech sellers.
For instance, suppose a small nation agrees to five tech deals, each of them promising the delivery of 100 technology for 3 million dollars. That nation then buys 50 tech, and sits on most of the rest of the 15 million, and starts paying bills every day. Ten days later, the nation sends 50 tech to each of the five tech buyers, and rebuys the 50 tech five times; this should cost roughly 4 million dollars. Then the nation waits, say, eight more days, paying bills every day, and spends everything but the 4 million needed to rebuy the technology the second time, and then collects taxes. Then that nation has acquired about 6 million dollars of infrastructure and improvements, but hasn't had to pay bills on any of it for 18 days. This is very profitable.