Planning Poker is used for the group-based estimation of sizes, usually the effort or complexity in development projects. This is exactly how the value (business value) of features or products can be estimated.
But why "group-based"?
The anchor phenomenom makes it difficult to get real, individual assessments in group-based discussions. The anchor problem means, that the assessments by all discussion participants are subconsciously biased to the assessment of the first one, who initially explains his opinion (anchor). To avoid this effect, everybody has to make his individual decission secretly before sharing it with the other group members. This is exactly what planning poker cards are for.
Just follow these simple and clear steps to successfully play Delegation Poker. It is best to stick strictly to it at the beginning and only change things if you really understand the system.