[robocat]

Only if you are using pointers/slices into the buffer as an optimisation.

Otherwise there is no need to keep a buffer of anything after it has been parsed.

[marginalia_nu]

I'm talking about during parsing.

Let's assume I send you a JSON object that is one very long string and nothing else. It's e.g. 1 GB in size. To know you need to allocate a 1GB buffer, you need to first scan it, and then copy it; or keep reallocating the same buffer until it fits.

It's an absurd case, but shorter strings face similar overhead.