Also ability to send password reset emails to client if client requests it.
I can imagine it like this:

At checkout front desk lets client know they can book their next appointment online. "OH WOW didn't know you can do that"

Yes Linda, I can send you a welcome email with a link on how to set it up to your email address if you'd like!

Email sent with Welcome to Blank Salon online booking, thank you for being a valued clients etc etc.... Here's your token to set your account up.

Or sent via SMS as a link as well. linked so that when account is set up, some token system recognizes that the user set up is the same as the message sent from boulevard to reduce the chance of creating a new user that would result in redundancy and needing to manual merge later.