What's the advantage of using bitcoin to buy coffee? Why would an average consumer prefer bitcoin over fiat options like credit card and ApplePay to buy coffee? Even assuming bitcoin transaction fee is minimal and instantaneous (say, after implementing Lightning Network), is the 2-3% transaction fee reduction worth paying with bitcoin, given its drawbacks such as volatility and lack of chargebacks?
There are billions of people that don't have access to credit cards and banking facilities that the privileged people take for granted. There are also people that get into financial trouble and lose all credibility in the banking system. Bitcoin provides a way for these people to transact without being part of the banking system. Coffee, however is a very superficial use case. One of the pressing needs is for people to send money back to their families in foreign countries, the current system of international payments makes it extremely expensive and very slow, Bitcoin and the lightning network can really help in cases like these.