Source: Administration Workshop II 8-14.

To be taken into account when manually tuning the pool sizes:

• OLTP systems require large buffer cache
• Parallel batch jobs require large value for large pool

Now, it’s typical to have a system that runs large OLTP jobs during the day (requiring a large buffer cache) and runs parallel batch jobs at night (requiring a large value for the large pool). In this system you would have to simultaneously configure both the buffer cache and the large pool to acoommodate your peak requirements, if using manual pool sizing. This means wasting memory. Using Automatic Shared Memory Management (ASMM) you would maximize memory utilization by automatically adjusting the pool sizes.