Why Online Study?
Spend less time mastering a topic : why read those 20 pages twice or thrice to understand a topic if you could just scan through a well designed presentation and be ready for an extempore or chapter test next morning?
Retain what you learn: text books are great for learning the details but often, you have little or no time to refer to the text books for every other topic; when you need to prepare for the exam and have less time at hand, online study notes can help a great deal.
Shorter learning curve: study notes are prepared mostly by faculty members and students who have been there and done that. So you’d basically be spending less time traversing the learning curve.