Being able to receive RTP streams is necessary for several types of applications.
For example:
Conferencing applications need to be able to receive a media stream from an RTP session and render it on the console.
A telephone answering machine application needs to be able to receive a media stream from an RTP session and store it in a file.
An application that records a conversation or conference must be able to receive a media stream from an RTP session and both render it on the console and store it in a file.