Why only apps ?

All the pl/sql packages will be created in APPS Schema
All the views will be created in APPS Schema
For each table in individual schema, there will exist one synonym in APPS schema
Tables are not created in APPS schema.
Every implementation has at least 1 custom schema, where custom tables are created.
For each custom table created by you, you will need to create a Synonym in APPS schema
As a developer, you will either connect to APPS Schema or to the custom schema where you will create new tables.