It depend on if it's a good fit.
When deciding whether to bid on an RFP, we treat it like any other incoming project. If it looks like a good fit for us then we may choose to submit a proposal in response.
Typically, RFPs are issued by large, slower-moving organizations and bureaucracies such as governmental entities, military contractors, and large businesses in lagging business sectors. Their project requirements may, or may not be a fit to an agile, fast-moving, responsive PPC agency but frequently not.
We do give all RFP's a serious look before deciding whether to participate.