Certainly masking hides outer edge lens irregularities. Thankfully lens technologies have got much better to the point edge to edge crisp images are pretty easy to do well.
Another reason for masking was to lessen scope body interior reflections bouncing about. Cheap scopes can have some pretty rough interiors which isn't helpful.

That Redfield is what I was thinking of. Maybe a few badged that design?? In truth those with such a design had pretty good glass.