That will be very specific to each business and each consumer.
That's a big problem! Fiat currency is universally useful to to every legitimate business and consumer, and btc needs to be as well if it's to have a long-term role in the world.
Hmm...got quite a few dollar bills in my cupboard from my last visit to the US...but they don't seem very "universally useful" to me at the moment...?
Unsure where you live, but unless it's on a deserted island, you have money changers you can reliably take your dollars to and convert into your local currency. If you live anywhere near an urban area, you have dozens of hundreds of options, whose reliability may vary not much at all (Europe/US) or widely (2nd and 3rd world). Regardless though, you'll have many options.
Part of a currency's value is in how universally it is accepted as a storage of value, and the dollar is way up there. Bitcoin has a very long way to go to becoming universally recognized, much less universally recognizes as having value.
Yes I can also convert Bitcoins into my local currency, so why are USD universally more useful to me? I can't buy anything with my dollar bills (or is there a slot on my computer somewhere that I can push them in?)
I can buy things with my Bitcoins, I bought a domain from namecheap yesterday.