I think that high density is associated with a sustainable urban pattern because it allows a more intense use of urban land. So basically a great number of people can use the same footprint. There are degrees of urban density patterns, and the denser, the more complex it gets to lead with the density and building stock.
What are the challenges of high density?
In my opinion, high dense projects and districts have to face challenges related to the provision of services, urban impact on the built environment, social integration, management and maintenance cost, and natural hazards.