It's helpful to think of your property as a living system. Within this system is a complex set of relationships among soil, water, plants and animals. There's also relationships between your property and the surrounding, neighboring lands. This is where the site assessment comes in.
A site assessment will determine obtainable goals for plant and animal communities on your property, within the context of surrounding lands and irreversible human-induced land alterations. The assessment will identify which relationships support the desired plant and animal communities, and which are working against it. It is important to get this "system" design correct from the beginning. This helps set reasonable land management timetables and expectations, avoids frustration, and prevents wasting valuable time and resources.