USEFUL INFO
What a script editor does
A script editor doesn't rewrite someone else's text: they understand what that text is trying to do, and clear away whatever is stopping it. It is a craft of reading before it is a craft of writing.
What they do, concretely
They read. A lot. Then they work out where the reader is lost, why they are lost, and how to win them back.
This is obviously the start of a conversation, not a verdict. We go through what isn't working together and, only if the author agrees, the text gets changed.
How they differ from a co-writer
A co-writer writes; a script editor doesn't: they touch the text only if asked, and only as far as they are asked.
It is a difference worth putting in writing before starting, because “give me a few notes” and “fix it for me” are two different jobs, with different timelines and different prices.
When it is worth having it read
You know when you work so hard on something that it looks perfect, and then you look again two days later and think it should all go in the bin? That is where a script editor saves you time, essentially.
So that it is ready to be sent out.