In this page you can view every customer you have in the system, whether they have an active mandate or not and if they are linked to Xero or not.
You can find out just about everything about a customer from here. You can also see when the customer list was last synced from Xero (see screen shot below). At any time in the day you can also click to Sync from Xero there and then and, within a matter of moments your list will be updated.
From here you can also hop straight over to Xero itself to view the customer in full. This can only be done on those customers that are linked to a Xero already. Simply hover over the tick in the 'Linked to Xero' column to redirect you to the customer record within your Xero Dashboard.