Final answer:
PIM-SM is utilized when there is a low number of routers with attached members compared to the total number of routers on the internet, making it suitable for sparsely distributed multicast groups.
Step-by-step explanation:
PIM-SM (Protocol Independent Multicast - Sparse Mode) is used when the number of routers with attached members is low relative to the number of routers in the internet. This multicast routing technique is designed for efficient routing to dispersed systems across large networks. The term sparse refers to the scenarios where there are fewer members interested in the multicast group, hence making the protocol optimized for environments where group members are scattered across a wide area and group membership is sparse.