This has ties with why fiat currency runs a portion of our country.
If everything went onto an electronic credit system, your proof or purchases or what you bought is always going to be visible to someone. Like minority report style. This is probably going to become the future, no doubt at all. Whether or not it will occur during our time is a different story.
For one example, say you buy some products for cheap in Europe and resell back in the states for high. The IRS will catch on with your business and you can't use the flexibility in earning money any longer; people will have electronic records of what you do.
Using paper money, it's harder to trace and most of all guarantees privacy, even if the business isn't illegal.
With that being said, that's one of the reasons why privacy still exists.