Just by adding an extra shelf halfway between the floor and your current shelf you essentially double the capacity of your closet.  Typically new homes are come with one wire shelf which you can hang one row of shirts and pants on.  Underneath the length of this clothing however there is a lot of underutilized space.  People have more stuff than they ever have before and this is one way to help solve that problem.

Just think how much your significant other will appreciate that.