When modern people think of imperialism, the practices of slavery and racism come to mind; while those are among the cons of imperialism, the institution also ended up having some benefits, particularly among the countries that were able to settle colonies elsewhere. The principle of self-determination for countries is more in line with the claims of democracy, making the rise of new empires extremely unlikely in the 21st century.
For the European colonial powers, the benefits of imperialism included money from captive buyers, cheap labor, natural resources from the colonies and new cuisine. The world developed a global economy, and capital from profits in the colonies went to invest in new technologies that would benefit the entire world.
For the areas that were colonized, the benefits included a modern monetary system, access to new technologies, hospitals and schools, the elimination of such harmful traditions as foot binding, as well as a modern infrastructure with rail lines and modern communication.
For the European powers, the major drawback of imperialism was greed, as the growing rivalries among the countries led to fighting, almost from the beginning of the age of exploration until the outbreak of World War I. All of these conflicts sprang from grievances in the formation of colonial empires.
For the areas that were colonized, the cons were many: disruption of traditional culture and economy, a heavy tax burden to the colonizing power, men having to leave families behind to work in mines or on plantations, the development of sweatshop conditions and a political system that crashed into chaos after independence in many cases.