How can high population density be helpful to a population?

Well, a high population density isn't really good at all. Alot of Canada and our world aren't even used at all. And almost all the people that live in Canada are crammed into Ontario, giving us the highest population density in the country, yet if you look to Prince Edward Island, the population is about 75,000 people more than Northwest Territories and Nunavut combined, yet NWT and Nunavut cover almost a third of Canada's land. But on the bright side, it can help a city get on the CMA list (Census Metropolitan Area), which is a city over 100,00 people. And it does help with industrialization and the further urbanization of our world.