In what cases would a Request for Proposals (RFP) process be used?

A Request for Proposals (RFP) asks artists to create and submit plans for the production of a desired public artwork.  Those plans are then evaluated by the commissioning organization, which makes their selection based upon the proposals.
RFPs can be an effective way to consider and evaluate the suitability of an artist when a limited number of artists are invited to participate in the selection process, the criteria for selection is explicit and uniform, and there is an honorarium paid to each artist for each submission.  Proposals should only be requested when the commissioning agency or organization is prepared to consider the proposal as a conceptual approach to the project and not the final design.  The commissioning agency should also ensure the artist retains copyright of all ideas presented as part of the proposal, even if those ideas are not ultimately selected for the commission.