Why donate with crypto in general?
Cryptocurrency is an asset, a little bit like shares in a company. Cryptocurrencies are traded just like shares, and have value that can be expressed in terms of regular (fiat) currencies, like USD or GBP.
You could always just sell some of your cryptocurrency (i.e. converting the value back into a regular currency), and then donate the proceeds. However, it might be better to donate the cryptocurrency instead, for two main reasons.
Firstly, it’s usually more tax-efficient. Because cryptocurrencies are an asset, selling them (and making a profit based on what you originally paid for them) incurs capital gains tax (CGT) in many jurisdictions. If you instead donate the cryptocurrency, you’ll avoid a capital gains event, which means you won’t have to pay CGT on those profits. (This shouldn’t be treated as tax advice, and you should check what the relevant laws are in your country.)
Secondly, it’s simpler: If you already own cryptocurrency, then it saves you the extra hassle of going to an exchange, selling your crypto, waiting to withdraw the proceeds, and then finally making a donation.