The big pro for basing off another Pivot Table is the reservation of
memory. The big con is that both are linked. This means much of what you
do to one, effects the other. Perphaps the one that most get caught with
is the 'grouping' of data. Group one Pivot Table and any others based
off it will also be grouped.
I will often base one PT off another to save the user from having to
drag fields about.