Tact helps you to check if your message fits the limit and if not - it will suggest to use a special type modifier bounced for the receiver that would construct a partial representation that fits into the required limits.
But the types section needs this info for the sake of completeness
This is explained in https://docs.tact-lang.org/book/bounced#bounced-messages-in-tact:
But the types section needs this info for the sake of completeness