Here is an example:
My best friend doesn't see the advantages of Bitcoin.
When we talk about the currency or mention numbers and quantitates of the asset, the word should be spelt with a lowercase b.
Here is an example:
I sent my best friend 1 bitcoin as a birthday gift.
Do you pay attention to this while you are posting on the forum?
I think this is about difference in semantics. The difference is not closely felt but with the example I see that the first is pointing to the name bitcoin and the second is about the digital currency.