Doesn't "lines" make more sense as the unit you measure the import rate at, or no?

99% of the time, yes, but it isn't very good for testing Harbormaster's behavior when you pipe a lot of of binary garbage with no newlines inside it (e.g., head -c99999999 /dev/zero | ...), or pipe in half a UTF8 character at a time so that the log continually ends in the middle of an emoji or something like that. I only expect this flag to be useful for testing/development and want it to be able to test those cases, and a byte-based rate can surface those better than a line-based rate.