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

500 Euro bills show up in action movies as part of shorthand for shady dealings. Like a visual cue that something is not on the up-and-up.

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.

I mean nowadays sounds just like much less hassle to use crypto for this use cases.

Unless you have unclean cash to clean ofc