My trusty copy of "What's Where in the Apple", which includes a catalog of where everything is in memory, says that the routine to write the VTOC from its in-memory buffer to disk starts at $AFF8.
The VTOC is the volume table of contents (https://en.wikipedia.org/wiki/Talk%3AApple_DOS#Volume_Table_...), so calling into the middle of that presumably ends up overwriting the VTOC with junk, which would indeed make the disk useless.
My trusty copy of "What's Where in the Apple", which includes a catalog of where everything is in memory, says that the routine to write the VTOC from its in-memory buffer to disk starts at $AFF8.
The VTOC is the volume table of contents (https://en.wikipedia.org/wiki/Talk%3AApple_DOS#Volume_Table_...), so calling into the middle of that presumably ends up overwriting the VTOC with junk, which would indeed make the disk useless.