[hluch]

There are several use cases.

1. Paying merchants who don't accept any other cryptocurrency (which is the majority of the available ones; typically they accept fiat in some form, plus Bitcoin since it's been around so long, but have barely heard of others).

2. Donations, same as above.

3. As an onramp from fiat to other cryptocurrencies, where those are accepted and Bitcoin BTC transaction fees for 1 confirmation in a reasonable time are an excessively high portion of the transaction amount.

4. For cryptocurrency payments which need the very highest possible level of security against double-spends, which is provided by Bitcoin's hashrate and decentralization, arising from there being a mature community around it. As far as I can tell, none of the other currencies have equally good metrics, though they do approach it.

Plus a few more.

And not forgetting that Bitcoin Core could in future raise the block size, making each unit increase sharply in utility and value, beyond its natural deflationary increase.