Executing a legacy script through php ezpublish/console ezpublish:legacy:script will output the following in the first line:

#!/usr/bin/env php

The above should not be displayed, even more so when the scripts are given the '--quiet' option.
Another use case would be if the output needs to be in a certain format (such as JSON), in which case the line will break the format.

Note:

This output originates in the shebang line on the actual legacy scripts, that specify the php interpreter to use.