Galaxy S Tablet microsd question (related to Logos on Android)

Hi

I bought an Android Samsung Galaxy S Tablet to run Logos app on it and notice it has a slot for microsd on the side of it.  Anyone got a reason why Logos app would make use of extra storage or know if we can download every book from Logos onto the card somehow please?

Not that up or hip to storage and I am curious how Android Logos could or might make use of extra storage via the card I could buy or insert.

Suggestions much appreciated please.

Thanks.