If you already have Automated Payments switched on each new customer will default to this option. However, you can from the customer page, switch off automated payments for each customer, individually.
For example, if there is customer you do not wish to bill for the next few months, simply click on the button (3 blue dots) along the right hand side as seen below and turn off. If your customer does not have an active mandate, clicking on the 3 blue dots will give you a unique link to send to your customer to set up a mandate or, an email reminder.
When Automated Payments is switched on from the Xero Automation Tab, all customers we default to have Automated Payments switched on. When globally Automated payments are disabled, the individual Automatic Payments toggle is ignored, and no payments will be created.