The difference is that if you plan work in one year increments you might be able to avoid conflict for 9 months to a year. If you're a really good avoider you might even be able to get some work done.
With agile you're certain to have an argument, butterflies in your stomach and other unpleasantness in every sprint -- and you'll be blaming your process for your problems whereas with a lack of process you'll blame something other than your process.