First, it is important to define what a value chain is. In short, a value chain is the process by which a company brings a product or service from its beginning stages to fruition. This includes things like, marketing, sales, customer service, to name a few. More importantly, a value chain seeks to minimize costs and maximize profits by thinking of innovative ways to streamline everything. The idea of a value chain was popularized by Michael Porter.
In terms of motivations, all companies want to maximize profits. So, if they can do this by making things more effective, they will do so. In addition, all companies want a competitive edge. So, if they can be more effective than their peer companies, they will seek to do this as well.
In terms of conditions, I am pretty sure that profits are wanted in all conditions, but I would say that value chains are more important in downturns of the economy.