You often want to be able to have an email go to a customer (contact) based on a workflow event.  For example when a service request is logged or changed, thus keeping the customer up to date. From R16 this is now possible using the JoinFieldValue function.

This function basically pulls  a field value from a related record of the current record.  For example the contact email address for the primary contact on an SR.  Now with the ability to define the email address in a workflow as an 'expression' it is possible to have a workflow email be sent to a contact. Until R16 this was only possible to a CRM On Demand User.

The trick is the configuration of the email address expression with JoinFieldValue. You can see in the screenshot below of the email action in a workflow  triggered for a change in SR status.

Here you can see the use of the expression builder for the email address, when 'Specific Email Address' is selected.  The expression I used is a nested JoinFieldValue;

JoinFieldValue('<Contact>', JoinFieldValue('<Contact>', [<ContactId>], '<ContactId>'),'<ContactEmail>')

This looks up the contact email address for the contact from the SR ContactID field.  You can edit this for other objects too like accounts, opptys, you just have to change the inner JoinFieldValue expressiion.