When is it appropriate to consult with the publisher/editor prior to manuscript submission?
This really depends on factors such as the field, the reason for contact etc. In my experience it is usually appropriate to consult with the publisher/editor in two cases, when:

(1) you have a short question about something that is not answered in their submission guidelines, or;

(2) you would like to send them an abstract to determine whether they think the potential submission fits with their journal.