The Default Settings page allows you to define a set of default settings that all new clients that you create will be set up with. This can be used to disable access to certain settings (i.e. VAT options, dropbox) or if your based outside the UK to create clients with your local settings (i.e. currency code, tax names). Similarly you can copy parts of another clients account (i.e. suppliers, products). Access this by going to Iris KashFlow Connect> Clients > Default Settings.
You can still set settings on per client basis by going to Clients > Edit Details next to the client.