I have a treadmill at home. I prefer working out at home because I don't live in a comfortable place for running outside (lots of cars all around).
There are also benefits in running indoors. You can track your progress much easier that way. When I run outside I don't know how fast I run, because after awhile you tend to slow down your pace ... well then, on the treadmill you can't slow down your pace unless you make the treadmill to slow down. That way I continue running at the same speed as at the beginning without slowing down (: even if I feel that my legs can't take it anymore..
But when I finish, it feels so good!

I must see my progress in order to keep my motivation running up.