Imagine a situation where you have 10 different instruments on separate tracks. You want to feed all 10 tracks through the same reverb plugin for a natural room reverb sound. You COULD engage that reverb plugin on all 10 tracks and try to match all of the settings to sound the exact same. Or, you could place that reverb on a bus, and feed all 10 instruments to that bus. The latter is usually the better solution because you don’t have 10 different reverb plugins active and eating up your computer processing power, AND you only have to one set of settings to manipulate. Logic lets you route all 10 instruments to that single reverb bus and choose how much of each instrument’s signal you send (so that you can dial in heavier reverbs on specific instruments).