What happens if I select more than one item template?

If more than one item template is selected, they will be applied sequentially.

It means that if the same attribute is defined in more than one template, the value of the attribute as set in a subsequent template in the sequence will override the previously set value for that attribute. For example, if template 1 sets the Order Enabled attribute to Yes and template 2 set the same attribute to No, then attribute value will be set to No.