The Oracle package setup with the "PRAGMA SERIALLY_REUSABLE;"
feature is "stateless" in Oracle 11gR2 (release 11.2.0.2 and higher),
which means packages can be recompiled without getting ORA-04068 
error ("existing state of packages … has been discarded").
 
The package state gets stored in a small pool in the system global 
area (SGA), thereby the state of the package persists only for the 
life of the server call or the session. The benefits of this feature 
are better memory management and improved scalability.  

The ceveat is that, procedure in SERIALLY_REUSABLE package cannot be
used in a database trigger or in a PL/SQL subprogram invoked by a SQL 
statement.

Packages not using this feature get stored in user global area (UGA)
for each user resulting in UGA memory consumption linearly with 
multiple users thus limiting application scalability.

Other features are:

Constrainted Datatype - SIMPLE_INTEGER

Constrainted Datatype - SIMPLE_FLOAT

Dynamic SQL - Execute Immediate CLOB

Caching Function Results - Results_Cache

Loop Forward With - CONTINUE