The survey produces a legal description of the property, which is more precise than merely a street address. It identifies the actual boundaries of the property, encroachments onto this property or from this property, how close buildings are to legal setbacks, where utilities cross the land, and the actual property lines.
A survey is used by the title insurance company because the title uses the legal description of the property. The survey is used to determine if there is an easement or an encroachment by another onto the land. Legally, these things need to be addressed in order to obtain a clear title. The survey is also used in new constructions to make sure buildings conform to local building ordinances.