What is the difference between a single db with lots of schemas -different apps and PDB in 12c

Hi experts.

What is the difference between a single db with lots of schemas -different apps and PDB in 12c?

For me Pdb in 12c is complicating things because it needs a system sysaux tablespaces for each Pdb and it acts as a separate db.

From:  Oracle 12c New Features - Oracle Solutions - Enterprise Solutions - Dell Community

The multitenant architecture enables an Oracle database to function as a multitenant container database (CDB).

Container Database (CDB): Every CDB has one root container (CDB$ROOT), one seed PDB (PDB$SEED) and zero or more user created PDB’s.

CDB$ROOT: it is exactly one root for each CDB which stores oracle supplied metadata (data dictionary) and common users.