its more of distraction and "disturbance". And it also helps push back the deployment spot of the CC castle, since CC castle cant be spawn on decorations.
Here is a defensive replay I made previously.
Watch at 1:20 how the wall breakers walk around the decorations hehe.
I've gave up trying with decorations though, just using it to increase cluster, nothing more. but maybe you can make decorations work ? haha.
https://www.youtube.com/watch?v=C1eHDDw_vlI&list=PLUYDE7MiyjxJHs94whuJnBs5-DL_AB4Dv&index=49