> (--checksum is essential to prevent corruption/malicious modification, without it you are implicitly assuming the version on the remote machine is exactly how you left it: that assumption is why Linus built git around shasum in the first place)
That's not true (though not completely wrong).
rsync is stateless. It does not assume the version on the remote machine is "exactly how you left it"; Rather, it compares file size and file modification time; if either changed, it will do a transfer -- efficient delta transfer, usually - which might be as little as 6 bytes if the contents is exactly the same.
--checksum makes it ignore file size or modification time, and compare the file checksum in order to decide if it's time for a transfer (delta or not).
A malicious actor, or bad memory chips, might change your file's contents, but keep the file size and time/date the same. In that case, --checksum will overwrite that file with your source version, and a --no-checksum wouldn't. So it's not bad advice. Whether the cost in disk activity is worth it depends on your thread model, data size, and disk activity costs. (Though, if corruption is due to bad memory, this is the least of your problems)
However, a corruption because of a program error / incompetent edit to the file is very unlikely to leave both the size and modification date intact - and a standard rsync will figure that out as well.