Condiments can be used either to bring out the taste of foods by contrast or to cover the flavor of foods by overpowering them. Which one you're doing generally depends on dosage. Eggs, like poultry meats, don't have particularly strong flavors of themselves, so easily lend themselves to being augmented with other flavors.
(My dad used to always put ketchup on his fried eggs; I currently find that works best with both a runny yolk and accompanying hash browns.)
