In Centazzo and Vitale's _A Duality Relative to a Limit Doctrine_ (TAC, 2002, [abstract](http://www.tac.mta.ca/tac/volumes/10/20/10-20abs.html)), early on, they make the above claim and cite Kelly's _Basic Concepts in Enriched Category Theory_ ([TAC reprints](http://www.tac.mta.ca/tac/reprints/articles/10/tr10abs.html)). I am having difficulty finding exactly where these general reasons are. 

Two questions: 

(1) What exactly in _Basic Concepts..._ are they referring to?

(2) What is an explicit formula for this specific left adjoint?