During preparation day everyone is bored and ready to get the battle day started. To fix this problem supercell should make it were everyone can battle clan mates bases.Testing there defenses and seeing what works and what don't. I don't think it should it effect loot or take away anything but it would be super fun to attack each other. Everyone in my clan is always bragging about designs they make I just think prep day would be a great way to attack clan mates without taking loot. Also maybe they could add a troop feature in prep day so u could make a army in prep day and it not cost elixer. So the attacker doesn't lose anything so it's all for fun.