Empirevr, You are correct, they do benefite the stringth of a break top firearm. Any addtional lock-up plays some part in the overall stringth of the rifle. Some do more than others, however, and none do anything if not fitted properly. I think if I had to choose one as more benificial, it would be a well fitted doll's head. The doll's head with the addtion of a bite is even better, and the screw grip on a doll's head is better yet. The best hedge against an "OFF FACE " condition is propper fitting in the first place of the barrels to the action, and the tight fitting of the lumps, and henge pin/lump hook, with proper care in the lubrication of those surfaces.
There are may double rifle with only the double bite under lumps, and hook/pin mateing that have survived for 100 yrs of use, without going off face, but those were properly fitted,by the maker, and properly cared for by their owners. Still some of the third fasteners are simply camoflage, and do nothing at all, but these are usually on cheap shotguns, and some bargain basement rifles. What it all boils down to is the individual firearm/maker,in the final analysis. Usually if the rifle is a well made example, it can be relied on to remaine tight, with proper care regardless of the number of fasteners!