[valdiorn]

I book my hair appointment online. they ask for name, email and mobile phone number. They need the name to know who to expect for the appointment. They ask for email and/or phone to send you a reminder (which is nice, IMO).

Very reasonable and totally with the GDPR rules as well, as long as they purge the data after a certain time.

[samus]

Email and phone number should be optional though. People can set up reminders on their phones by themselves.