This forum link where it was born seems to suggest that it's needed as a replacement for hooks or to be able to filter them in drupal views. But it seems you can make a view that filters based on end dates in the past, and there are hooks for relationships (maybe there weren't at the time of the original post).
An alternate way of asking this question is "what does is_active mean for relationships"? Is it just a stand-in instead of using effective-dating queries such as are common in PeopleSoft or HR systems (which have broader use, e.g. list all the people who were active employees in 2019)? Is it just a redundant data field that means "end date in the past"?
Besides trying to understand whether it's redundant and maybe a bit fragile, one reason I'm asking is that anyone who's using this scheduled job would be dependent on the fact that civi ends relationships when it does, and so a change to that would affect this. So another way of asking this question is "Is anybody using this scheduled job and can describe your use case a little bit?"