Hi identityreative,
every user that uses Taxi Booking has to be registered to your website so they can access their orders at any time, receive emails for Order status changes and have their orders stacked up to the same account.
If a user is not registered Taxi Booking will automatically create account for them and send them randomly generated password that they can change after log in to your website.
If a user with that email already exists Taxi Booking will stack orders in their account and will not create new user.
The only thing that can be done is a setting at the back end that will disable email sent to the user but registration will remain as per reasons explained above.
If you really prefer not to send Registration information to your users we can create that option for you but it will require custom development.
Hope this answers your question.
Best regards.