Oracle have published a white paper entitled: “With Oracle Database 12c there is all the more reason to use database PL/SQL” it’s author is Bryn Llewellyn who is the Product Manager for PL/SQL.
In this paper Bryn lists the reasons he hears from customers on why they are not using PL/SQL in the database and then methodically sets about demolishing each of these objections.
It is an accessible, interesting paper and well worth reading.
As Oracle have a habit of periodically changing (breaking!) their links you can download the paper from here.