Client value is the total benefit (tangible and intangible) that you, your business partners, and your coalition provide a company throughout the life of the relationship. (Personally, I believe client value is NOT created or sustained by cutting costs to increase efficiencies, or by Cheap Cigarettes Outlet propping up share price through buybacks, spinoffs, or mergers/acquisitions.)
The concept of client value requires a bit of guessing and new thinking. Especially for people who are running a new business, working in a financially-driven (versus a sales-driven) culture, or haven't been keeping close track of customers, estimating the lifetime value of a client may require a bit of groundwork.