1. When we choose the basic installation, Windows Internal Database(WID), a relational database based on SQL server technology, is installed for the WSS3.0 databases. This WID has only 4 GB limitations. While if we go for advanced search, WSS 3.0 uses installed SQL server for the databases.
2. When we use basic installation, application pool uses the LocalSystem account.
3. Also once we go for Basic installation, we are unable to add more servers to the farm.