I don’t think there’s really a number for it. I usually prefer to see if my accuracy stays up. Usually a big part of the items we get wrong are our leeches after all. So I always try to give a quick review in the summary page after reviews.
But reviewing leeches is always a good thing imo. Here’s which scripts I use:
You can review them every day or choose one day that you have more free time. I used to do the former but now I do the latter. It’s one less worry to have every day.