they famously called the 500 euro bills -bin ladens- for how hard they became to secure since all the unofficial transactions where mostly done with those high denomination bills
They seem to be of most use to rich people who want to hide assets from the tax man by carrying the cash across the border to Switzerland. Probably doesn't work as well as it used to anymore though. A few years back I talked to a guy from norther Italy who said most people had a second bank account in Switzerland to hide money from the government.