Regenerating and making cities more sustainable does not only mean "reinhabiting" cities or parts of them by reusing degraded buildings and disused industrial areas. It means limiting the delocalization of services by encouraging a more efficient reorganization of urban functions. It is necessary to optimize the functioning of cities, improve accessibility to urban services, and ensure the connection between public spaces. A careful reuse of functions and relationships with urban environments promotes sustainable mobility; the concentration of primary activities within the existing city reduces consumption and CO₂ emissions associated with the use of private transport, as well as urban lighting and maintenance costs. In this sense, urban planning plays a fundamental role, but not only that. Implementation and sectoral tools must be able to interact. In some countries, this is a recurring approach: making sectoral tools interact is a principle shared at all levels. The paper will identify selected case studies chosen for their relevance and for the contribution they offer, within the framework of urban planning tools, to sustainability through the optimal location of services and their 24-hour, day and night functioning. This all aims to reduce consumption and emissions. In Italy, the Municipal Public Lighting Plan and, where applicable, the Municipal Energy Plan, if integrated, can reduce consumption and emissions and optimize functions without sacrificing efficiency and aesthetic needs. It is essential that new functions be aligned with the transformation demands of communities, and that they be supported by well-organized services and infrastructures. It would be appropriate to assign new functions to areas with greater energy availability. The above-mentioned sectoral tools, through effective dialogue, would allow for a reduction in air, noise, and light pollution; an improvement in the energy efficiency of systems; and an optimization of operating and maintenance costs.