Well, there are some examples where, under certain circumstances with other plugins where creative placed ores will still drop items from other plugins, and vis versa. Or if you loose your data, they can all be mined. Also, most builders don't utilize or never need to place such blocks so kinda just a fail safe. Also things like shulkers and beacons can be used if placed. This can be harmful if you have survival and creative players coexisting. And a lot of other misc reasons after examining things throughout several years. I think it heavily benefits from blocking potentially too much, rather then not enough and finding yourself trouble down the road.