Convenience, I guess. I do not do it often, but when I do it's because the product(s) I am looking for are not available in my area or country. Then I resort to the internet. But, like I said, I don't do that often. I used to buy books on http://www.amazon.com
when I was in college and we were asked to buy books in English and unfortunately they were not available in bookstores, for instance.