Confused with Delta

Hi,

Newbie questions here...

1. How can i see if my data source is delta enabled?

2. Why basically all business content data sources are not delta enabled by default? What is the benefit of having them not being delta enabled?

3. What is the ODS role in a scenario that we extract data from a non delta enabled data provider to an ODS and then basically use the activated data table in the ODS for accomplishing delta extraction to an Info Cube?

4. Can some refer me to some good and deeper information on those??

Thanks.