But removal of suspended particles does not mean that the water is safe to drink. It only means there is less "crud" in it.

Removal of organics can make sanitizing chemicals more effective, especially for chlorine-related chemicals. I'm not sure if that is the case with iodine.

I suspect that water treatment plants use floculation (real word?) because it is more suited to large volumes of water than filtering - are at least more cost effective.