  Dimensionless ratios characterizing many-body systems are a powerful tool to
reveal the main universal quantities involved. The recently-introduced
localisation parameter allow to study the occurrence of crystal,
clusterisation, and quantum liquid states in many-body systems such as nuclei.
Its concomitant use with other dimensionless quantities such as the quantality,
allows to pinpoint fundamental lengthscales and dimensionless ratios at work in
nuclei. Within the present approach, the impact of delocalisation on nuclear
saturation is discussed. The transition from a homogeneous to a clusterised
state in low density systems is studied. The spin-orbit effect in nuclei and
fermionic systems is also reviewed in the light of this analysis. A generalised
localisation parameter is derived, showing that the delocalisation properties
are not always driven by the quantality. The concepts of quantum fluidity and
mobility are finally introduced.
