Originally Posted by
Defaultmp3
Batteries can die for reasons outside of simply running out of juice.
There's also the issue of environmental factors, such as fogging of the optics, occlusion by debris/scratches, etc. Manufacturing failures of an optic can also certainly be an issue, whether it be delamination, glue coming loose, springs breaking, etc.; the bathtub curve will probably solve that for any gun you shoot regularly, but it's still a possibility. I think there's a strong argument to be made that BUIS are no longer necessities for some optics (Aimpoints, ACOGs, etc.), but that's very different than saying that BUIS are now irrelevant/useless/a fashion statement.