its self explainatory
this block might be very useful for making stuff with diffrent forms
ex. a hammer that can change to axe or pickaxe mode on right click. But if you use set hammer form 2 in inventory, it won't directly go to your main hand, so its not very good.
I seen this done in many mods outside of mcreator
for example avartia, where there is this pickaxe which can mine either 1*1*1 or 16*16*16 (I know its op, but thats not the point)