db_fetch_size and scalable_mode options

 Was wondering if anyone could help put a bit more flesh on the bones of what affect the following options have on BI Publisher (5.6.3 running within Oracle E-Business Suite 12.1.1)  

<property name="scalable_mode" value="on" />--default off

<property name="db_fetch_size" value="20" /> ---default 500

 

The majority of our custom definitions (.xml data templates) have these values hard coded on them. I understand that setting scalable mode will use the disk and not actual  memory to render the output and db fetch size is the records across the jdbc connect. However I was wondering if someone had a bit more detail on them? I think the user guides don't really go into much detail on them. For example would removing them reduce run time and bring a performance benefit? If so performance of what the generation of the xml or the post processing actions? For example