Imagine, when an SMS arrives, that you do not have to stop what you are doing to see who sent it.
Maybe you are driving or busy, but want to know it the SMS is important or not.
That is what Hear SMSs does.
It tell you WHO sent the SMS and the CONTENTS of the SMS.
The SMS will also be found in your Messaging, as usual.
In addition, pulling down the notification bar and taping on the HearSMSs icon will display the SMS.