why schedule line category must needed

Hello Experts,

I gone through several threads in the forum but still confused.

I got the info like...

It confirms the

1. confirmed date of delivery

2. confirmed quantity of del

3. Availability check

4. Transfer of requirement

a.purchase requisition type

b. delivery block

c. movment type of goods

The Schedule line contains the delivery date and quanitity in a slaes document item. This is only a one line explanation for your understanding purpose only.Tcode VOV6.

..........................

Now please kindly explain me with an example without slc what will not happen.

one Item can have many schedule lines . Why we need many SLC for one item please tell me with example.

Thanks in advance for all the replies