The high interindividual variability and repeatability of several sleep state-specific neural oscillatory phenomena, as well as the strong bidirectional connection between sleep and cognition indicates a royal road to the insight in neurodevelopmental and neurocognitive profiles. On the oscillatory part of these correlations we find a preferential emergence of the phenomena characterized by direct associations with neural plasticity (mainly the sleep slow oscillation and spindles). Among the principal behavioural and clinical phenomena related to the phenomenological aspects of sleep state-dependent neural oscillations intelligence, sex differences, (a)typical development, aging, neurodegenerative disorders, and schizophrenia were found to be of outstanding significance. The individual oscillatory profiling of sleep is an emerging field of translational science which is characterized by a desperate need for methodological revision. In order to get insight in the practical aspects of the above detailed fields some methodological inconsistencies have to be transcended. My aim is to highlight some of these inconsistencies and provide easy solutions for fixing the related issues.