LeadSight only ever requests read access to your Xero invoices and contacts — enough to match leads to closed, paid revenue.
LeadSight cannot create, edit or delete anything in your Xero account. It's a one-way, read-only connection.
LeadSight also syncs your full invoice history from Xero, not just invoices created after you connected — so historical customers can appear in your reports too, whether or not they match to a specific tracked lead.