Salesforce is a popular and powerful online Customer Relationship Management (CRM) tool. Why did you integrate Drupal with Salesforce? Drupal is the popular Content Management System (CMS). The most use case is you can generate lead in Salesforce CRM by integrating Drupal with Salesforce CRM. You can send Drupal website contact/query form inputs to Salesforce and save data's in CRM records.
Using this method you can generate leads through Drupal Website. It's very easy implement and customize. Using AJAX you can post Drupal form inputs to Salesforce CRM without refreshing the page. AJAX will improve Website performance also.