People can get easily helps from intelligently autonomous mobile agents nowadays. The services from the agents maintain social function as a part of human-robot interaction (HRI). As the technical developments improve increasingly, there are still lacks of clarification of the social functions which the mobile agents can achieve, and relationship-discovery between the human beings and the agents subject to the HRI. From sociological aspect, this study seeks the sociological relevance created by this kind of HRI, and evaluates the corresponding social value by taking significant examples. Starting from a causality analysis between the social needs which the human beings desire and the accessible services which the agents can provide, this paper confirms first the value of navigating an agent to finish the service, and recognizes the navigation as one part of the interaction during the service. The core technique of this kind of robotic interaction monitors the dynamic changes of environment, provides an adequate route plan to reach the goal service, and reacts properly the environmental changes during approaching the goal.