Sending funds to family in a different country. It's a use case I have not had experience with but which I think makes sense.

Is it really cheaper or easier to buy BTC, transfer them, then sell them than to transfer money through a traditional service?

Faster and cheaper with segwit not sure what its like currently. I transferred 5k to someone in 40 seconds for like a 20 cent fee with Eth a few months ago, it could be 100k and the fee would stay the same too.

You also get the money immediately without it going through the ACH network.

That's if you already have BTC and the person you're transferring to wants BTC, but if you're simply using BTC as a way to transfer fiat money from one country to another, there are more fees and delays in the buying and selling.

The valuation of BTC is also a derivatives market of illegal activity, something which is not illegal itself.