Use of RSA3

Hello, I am little bit confused in using RSA 3 transaction.

1. As i understand - Datasource never stores data actually. It only use to extract the data and saves the data in PSA by running infopackage. - Plz correct me.

2. In LO extraction - Datasource could extract the data either from Set up table or from Delta Queue.

If you want to delete the data the Best practise is to delete the data from setup tables by LBWG and from delta queue by RSA7

3. What is the exact use of RSA3 transaction. Plz explain.

Thanks