In a service-oriented relationship, the focus is on how the submissive can contribute resources to the dominant partner, provide for some of their needs or advance their goals. These relationships may or may not also include romantic feelings.
A common example of such a relationship would be one in which the submissive and dominant were romantically attracted and the submissive is collared to the dominant, indicating that they are "in service" to that dominant. The collar may well be predicated on certain performance levels or the usefulness of that submissive in specific areas. If those things were to change or dissipate the couple may remain romantically linked but often the collar will be removed.
For the submissive in such a relationship, the collar is seen as a status symbol signifying the approval and acknowledgement of a person they wish to serve. They often take great pleasure and pride in their status and relationship.
For the dominant, the benefits are practical as well as emotional. Many take great pleasure in being 'served' in this manner, and of course having the additional resources available is of immense utility.