Array processing refers to Oracle’s ability to insert or select more than one row in a single operation. For SQL, which deals with multiple rows of data, array processing usually results in reductions of 50% or more in execution time (more if you are working across the network). In some application environments, array processing is implemented automatically and you will not have to do anything to enable this feature. In other environments, array processing must be totally implemented by the programmer.
Many programmers implement huge arrays. This can be excessive and may even reduce performance by increasing memory requirements for the program. Most of the gains of array processing are gained by increasing the array size from 1 to about 20. Further increases result in diminishing gains. You do not normally see much improvement when increasing the array size over 100.