Latches are simple, low-level serialization mechanisms to protect shared data structures in the system global area (SGA). Latches protect the list of users currently accessing the database, and protect the data structures describing the blocks in the buffer cache. A server or background process must acquire the accompanying latch to start manipulating or selecting a shared data structure and must release the accompanying latch when finished.
Latches are managed by Oracle internally. It cannot be tuned, but latch information can be used to tune the SGA.

There is no information in the Oracle 9i Performance Tuning Press regarding

2. Parse CPU to Parse Elapsd
3. Non-Parse CPU

Is it really that important, I dont think so, otherwise they wound have included it in oracle press.