This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
I suppose the answer is that by not having to redo the query, you save time. However, this is dependent on the scenario and involves a memory tradeoff. So it depends on whether it will increase performance.