As a Streamer, Diamonds are a great way to track your success. You earn Diamonds for your activity on the stream, unique visitors and reactions that your viewers send you.
A stream summary will be shown at the end of every Livestream. This will show you the number of Diamonds you've earned, the duration of the Live, the number of unique visitors and unique reactions as well as the number of gifts you've received. This should help you have a better understanding of your achievements as a Streamer.