To me, it's the portability. Try carrying large amounts of cash across a border, or even through airports within a country. No more expensive and complicated wire transfer requests, no more trying to hide cash in your baggage and praying that some TSA agent will steal it while your baggage is out of your sight (even as carry ons). I'm surprised that cash businesses (think casinos, especially) don't have some kind of BTC->Fiat "ATM" right in the casino. At least until they just take BTC for wagering, which may or may not be popular as most large gamblers prefer to remain as anonymous as possible.