I do it mostly to be consistent and its a easy way to remove one variable. There are so many variables with a ML and if you can remove even one it cant hurt. I would rather a load shoots consistently good or consistently bad while im trying to figure out what load the gun prefers.

Sabot fit is not that hard to figure out but the drag the sabot has going in and coming out could change enough to hurt/help accuracy if you have random petal to land contact.

I dont think indexing will turn a poor shooting load into even a average group but i do think it can possibly turn a very good shooting load into an excellent one.