Atom Economy

Wouldn't it be great if there could be an higher occurance of atom economy? That is, ending with the same amount of atoms that one began with when producing compounds and such. I've learned that there are several different classifications of reactions that can reveal their atom economy. Addition and rearrangement seem to have the best atom economy, both end with 100% of the atoms began with in the resulting product. Condensation probably comes after that, with slightly less than 100% of the atoms in the final product, and usually the waste is in the form of small molecules like amonia and water. Substitution was pretty vague. I suppose it varies in it's atom economy. Some very efficient, some not. Elimination seems to be the least efficient of them, since it always results in a byproduct.