Valuation of property as at a specific date where use of property may have changed. For example, house use changes from owner-occupier to rental property or vice versa. Retrospective valuations for Capital Gains Tax purposes are common for valuation of part of a property (eg larger land areas where the dwelling & 2 hectare surrounds are exempt from CGT - principal place of residence).
This means that you get the 'real' valuation of your real estate with no hidden agendas.