Document Controls and Defaults functionality option functionalities

Hi Folks,

Could some one clarify following doubts .

Document Control:-

1. Price tolerance

2. Enforce  full Lot quantity (Advisory, Mandatory, None)

3. Receipt Close point (Accepted, Delivered, Received)

4. Cancel Requisitions (Always, optional, never)

5. Allow Item description update

6. Gapless Invoice numbering

7. Enforce supplier hold

Document Defaults:-

1. Acceptance required flag (Document, None, Signature, Document or Shipment)

2. Line Type

3. Price Break Type

4. Price Type

Please explain each point with suitable business example to understand this setup screen.