understanding of Picking rule

 Hi,

I read about picking rule in many sites even in user guide,but doesn't found the purpose of this picking rule.

For the accountant who don't use oracle,how can i explain the purpose of this picking rule.

I have some question regarding this,these common questions are asked by interviewer many times :

1)What is picking rule and their Purpose

2)What is pick slip grouping rule and their purpose

3)What is release rule and their Purpose

4)Difference b/w pick slip grouping rule and picking rule and release rule?

5)Why it is mandatory to define these rule?

6)If we don't define these rule,what will be the impact?