It is important to understand how approval email notifications work in Salesforce.com, particularly when you are mass submitting/re-assigning approval requests. You might want to avoid unpleasant situations wherein users are flooded with email notifications in their inbox. This article tries to point out the various options available to avoid such situations.
How does Salesforce send an email to the approver when a request is submitted?
Note that even if you leave this field BLANK, Salesforce will still send out an email notification using a default email template. If you want to add your company branding to the email, this is the field to specify the template for it.
Some users tend to add an email alert as part of the initial submission actions. This might possibly send out two email notifications (Please test and verify).
How to stop email notifications while mass submitting/reassigning approval requests?
This is a rather pain some exercise since this has to be done individually for every user.
Navigate to the user detail page and set the below field to 'Never'.
Note : As of Summer 2015, this field is not available through the API and hence will have to be updated manually for every user.