This working paper develops the concept of sectoral efficiency as a structural premise for spatial and urban planning. Building on earlier work on deindustrialisation and post-sectoral transformation, it argues that sectoral change should not be understood primarily as a shift between economic sectors, but as a sequence of efficiency-driven reorganisations of production, coordination, and spatial logic. The paper introduces a phased model ranging from proto-product formation through segregation, standardisation, automation, and digitalisation, highlighting discontinuities rather than smooth transitions between stages. These efficiency phases generate distinct spatial consequences, including changes in location requirements, labour organisation, and urban form. Originally developed for an international academic conference and published as a book chapter in 2018, the contribution is presented here as a consolidated working paper to ensure long-term accessibility and integration into a broader post-sectoral research programme. Author keywords (free terms): sectoral efficiency; post-sectoral transformation; deindustrialisation; spatial planning; urban systems; coordination; automation; digitalisation. Internal reference: CB_04 (v0.1).