When we moved to Argentina in 2005 we rented a house for a year. The owner requested cash in U.S. dollars - all of it. I'll never forget sitting in the realtor's office while each and every bill was laid on paper to be photocopied so they would have all the serial numbers. What she did with all that cash, I really don't know. Maybe it went under the mattress or in a safe deposit box or some other special other hiding place. All I know is she wanted cash and nothing else.
This is the underground banking system so to speak. Argentines are reluctant to use banks since the economic crash and who can blame them when they saw their bank accounts devalue or disappear altogether during the crash. Add to this the high taxes and government "problems" and no one really wants anyone to know how much money they have or how much money they make. The major problem with doing everything in cash is the danger of carrying money around or keeping it in your home which increases the chance of being robbed or being the victim of a home invasion.
The IrishTimes.com ran an article called Living without Banking which I think gives really great insight into the dangers of keeping large amounts of cash on your or in your home (except of course unless you're the lucky one to find $300,000 but read the article to get that :))article.
If you're going to have to carry cash you'll always need to remember to take every precaution. Those precautions can include being wary of who knows what you're doing including people even related to a transaction because you never know who will talk about it and to whom.
Be safe everyone!