Dependency occurs when a local church [ed. or church planting movement] requires funding or leadership from outside of its own members in order carry out the core biblical responsibilities of a local church under normal conditions.
Consequences of financial dependency include a lack of ownership, stunted growth, mixed motives in leadership, confused accountability, suspicion of foreign influence, and compromised witness.
For a church to be sustainable it must be able to carry out its core biblical functions without relying on foreign funding or leadership.
The benefits of sustainability are the opposites of the consequences of dependency listed above.
In this masters thesis, Ken Stout does a great job of wrestling with the relationship between financial dependency and the health of a movement.