I think all it teaches my DD is that it's Ok to turn in a piece of ****, and get an F. You can always re-do it. Or not.
That is the same attitude in my child's school - homework is graded for "completion" and not "accuracy". So, as long as DS finishes his homework, he is fine. If I see busywork, I do it for him and tell him to go do something else that is useful to him or fun for him. I don't think that there is anything wrong in helping - exceptions are the cases where homework is meant to remediate the child's weaknesses in class.