To add to above, some of our materials (ceramics being one) the support material can be re-used. So we'd be sending out free material (seeing we only charge for material used) that we could be using to make someone else's model.
*you can leave the support material in Transparent Detail and FUD by having a tiny hole connecting inside geometry to the outside. This is allowed as the build material can be used as a visual technique with those materials. The Mad Moder