Sometimes, you see an interesting article on the internet, but you just don't have enough time to read it right now. You can close the window, but then you'll have to search through you entire history to find the site again--if you don't forget.
You can add it to your bookmarks, but then your bookmarks folder gets cluttered up. Bad options. Try Instapaper instead. It adds a tiny button to the top of your web browser. Whenever you click it, it saves the website you're on for you, so you can come back to it anytime. You can even export it to your iPad or Kindle, or create a neat printable version for a paper copy.