You can get reuse even with once per interaction configured on your datapage. For example if you have a lot of processing based on the datapage during an interaction. (say multiple stream rules show values computed from the same datapage) You can trace with Interaction and DataPage events to get a clear picture in your own application how many interactions occur, and how many data page loads it results in (and db queries can be traced too to get a feel for time and amount of data used if your load activity requires database access). This option will cause your datapage to be refreshed quite frequently, so please consider if it's appropriate in your application.
Also a clipboard page is an in memory structure, so on it's own will not be a database call. Your datapage may or may not use the database depending on your datapage load processing.
Still i am confused as every time i refer data page, it triggers DB as i query and place data on this page. So in this case if this page is used in multiple stream rules every time it hits DB. So what makes it better than clipboard page.