What is the purpose of payload in packet too big ICMPv6 message

问题

I have gone through the RFC 4443 and 8201, perhaps I did not understand as I am new to some terminology described in these RFC but I want to understand the implication of using payload in ICMP packet to big message?

As per the RFC 4443 Linkt to 4443 RFC

The payload will contain as much of invoking packet not exceeding the minimum path MTU in packet to big message.

I don't understand the use case of such payload, even in the RFC 8201 there is no mention about the usages of payload. only one comment present was

Added clarification in Section 4, "Protocol Requirements", that nodes should validate the payload of ICMP PTB messages per RFC 4443, and that nodes should detect decreases in PMTU as fast as possible.

What can be the implication validating payload in the PTB message and how should we validate the payload and based on what conditions?

Packet Too Big Message as per RFC 4443.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Type      |     Code      |          Checksum             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                             MTU                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    As much of invoking packet                 |
  +               as possible without the ICMPv6 packet           +
  |               exceeding the minimum IPv6 MTU [IPv6]           |

来源：https://stackoverflow.com/questions/59625922/what-is-the-purpose-of-payload-in-packet-too-big-icmpv6-message