There are some things that do go up in value after they are purchased. For example, the value of an education generally goes up every year. We can certainly earn more money with higher education. So, if it takes some debt to get an education it can definitely be worth the "investment". Likewise, buying a home is likely a great long term investment. Debt can be used wisely in buying a home. In most cases over a long period the value of a home will go up. location, bad neighborhood, flood, cracked foundation, etc are some examples of when a home may not appreciate. Tough economic times can also cause the value of a home to temporarily stay constant or go down in value.
The Moral--when you cannot afford to buy something that depreciates with cash. . . . .don't buy it until you save the money to pay "cash". Let interest work for you instead of against you.