The extension of "clinical depression" to include sadness created concern. Everyone feels down or sad sometimes, and usually, these moods pass without long-term consequences.
Clinical depression is more severe, such as losing sleep or thinking life isn't worth living and extends for a longer period. Lumping them together and ignoring the differing causes may lead to an inappropriate therapeutic approach.
This model also treats melancholia as a major depression "specifier" and not as a disorder in its own right.