Same point as zero sugar sodas... Enjoyment of the flavor even though it provides no nutrition or energy
It would be very helpful for keto diet stuff too, since breads are basically most of the carbs and calories you eat in a lot of meals
I do worry that much mass not being digested would be trouble for you though.
Depends. If it's sugar alcohols they can be a problem. If it's basically fiber, it depends on your microbiome if you do well on those fibers or not. (Also, some fiber like charcoal can be constipating.)