idle DB and resources

We've one site already in production and another one that will take
its birth from the previous one.
Since editors have to prune and adapt content from the previous one
I'm going to duplicate the DB and put it online on the same box and
let editors do their job.

Later we may decide to move it on another box or leave it there
since once the editors job will be finished the DB will be much
smaller.

Meanwhile we will have 2 large DB, one of them being nearly idle.
Is the idle DB going to have any impact on performance?

thanks

--
Ivan Sergio Borgonovo
http://www.webthatworks.it