If this parameter is set to true, the SalesforceConnection actually does not connect to Salesforce when you open a connection. It works with local data cache until you query data that is not cached or modify data. For more details, see Cache Overview.
A side effect of this may cause the following situation: if your connection string parameters are incorrect, but the data cache is present (for example, when your SecurityToken expires or a password to Salesforce account is changed), you won't get any connection errors when working with a connection till you work only with cached data. Only when you try to query data that is not cached or modify data, you will get the corresponding connection error.