Auto Assign Serial / Lot Numbers on SOP Document

When do we select this option in SOP Setup? Is there any valid requirement that would arise so we setup SOP that on a Sales Document, Serial/Lot numbers automatically get assigned?

I am talking about *Auto-Assign Serial Numbers* and *Auto-Assign Lot Numbers* options in Sales Order Processing Options Setup window.

As a normal practice, I would always keep it unselected. I would like to make sure that I handpick items with specific serial numbers so I won't let the system pick recent ones first and retain old ones.

Simply speaking, I would always want to sell old items first to make sure that I don't leave it in my stock as unsold. Like a FIFO.

There are prominently two queries that arise on my mind:

1. How GP automatically takes Serial/Lot numbers for a particular item, if we select the above options? Does it follow FIFO approach or does it randomly pick some serial/lot number?

2. Is there a practical scenario where we require these options selected?

I would be grateful to receive your inputs as comments.

Thanks in advance.

VAIDY