One of the beautiful things about running alone is that you can choose how far you want to run, how fast and where you want to go. There is no planning involved unless of course you want to plan. If you are out on a five-mile run and feel great and want to run farther, you don't have to check in with anyone to see if that is okay. Conversely, if it's just not your day and you want to head back home and try the run a different day, it doesn't impact anyone else.