If a recipe calls for a measuring of salt, very rarely is it ever a good idea to add all of it in the beginning. Cooking is a delicate process that requires continual attention and tasting along the way. Adding too much salt to a recipe is an easy way to overpower a dish and unfortunately, you can't take that salt away.
When you cook, you should salt as you go. If you finish cooking and your dish isn't just right, then you can add salt to achieve the desired taste. Simply put, salt is much easier to add than to take away.
The same can be said of ink. Primarily due to dot gain, ink is easier to add than take away. Dot gain is the phenomenon that is caused by halftone dots increasing in size during the printing process. A nice, round dot will grow on press as it is transferred to paper and the result can be an average 15% growth of the dot causing the dot to look darker than expected.
Unfortunately dot gain is unavoidable so printers must compensate by creating curves in prepress that eliminate the effects of dot gain. Because dot gain is greater in the midtone values (around a 50% tint) and less in the extremes (5-10% tint or 90-100% tint) a tint reduction on a linear curve is needed to lower midtone plate values. Simply put, you can't just lower the ink densities on press if the midtones are too dark as this would also result in the dark image areas to look light and faded. So to achieve the optimal printed image it becomes necessary to remove enough dot on the front end to compensate for the dot returning during the printing process.