ASA9 and multiple databases: best practise?

Hi folks,

I'm trying to find out the best practise when running multiple
databases. Most people seem to use the one-engine-multiple-databases
solution. I understand this to be best practise mainly for manageability
reasons. Sometimes a better efficieny in memory usage is thrown into
discussion - without giving any technical details. Could this be even a
question of licensing?
I would like to read your opinion on that topic. Maybe you have
knowledge of some white papers or usenet threads (I didn't find)
discussing that?

Kind regards from Bonn,
Claus Scherschel.
.