No matter how meticulous you are about oil changes there are areas inside every engine where oil doesn’t circulate well. The oil sits in depressions in metal castings of the engine where it slowly becomes thick and gooey from heat. Over time this forms chunks of sludge that move about inside the engine. As these chunks find their way to the oil pan they will eventually get pulled up into the oil pump screen where they will restrict the amount of oil that can circulate throughout the engine. Net result will be a shortened engine life.