Block inventory Max size of stack, please help

So while making other mods, I've noticed this feature Max size of stack on the block inventory section, and I was wondering if that is for how many items can be stacked in a single slot, I've been trying to do that, but it hasn't been working so far, maybe because that's not what it is. If anyone knows what is the feature of this and or how to use it please let me know, giving me some help would be much appreciated :)