I was asked this today due to a wrong spec on a job. The shade company required a 12-2 romex at each window shade location for power, so I did it. I went there today to start the install and reading the shade info it needs a 12-3 romex to work. The shade guy wants to use the ground conductor as a neutral and I told him no way no how. I am just thinking now though what is the real reason behind this. Safty because no ground? The current on the neutral now is not insulated on it's return trip?