Prompts/Layout Component reference/Query

[BiliBoy]

Hello Members

in our work environment we have been using good  numbers of prompt through layout component references.   can any one explain me when prompt is being used in your report through layout component reference then do i have to have query associated with prompt at both places in reference report and my report? what happened at run time, do prompt query try to hit database from two diffrent places(reference report and my report) or just from my report? does it really slows down your report, if its run from two different places?. it is advisable to use prompt through layout component refernces?

any one willing to share their knowledge and experties?