There are a lot of things that a good to-do app can do that "paper or a plain old text file" can't do. For example, it allows you to easily share that list with

There are a lot of things that a good to-do app can do that "paper or a plain old text file" can't do. For example, it allows you to easily share that list with others, set reminders that go off at certain times, etc. Google Now is pushing it even further by scanning your email for things you'll want to do without even knowing it.