Put them on outside exterior walls, even on walls next to your garage, and on outlets and switches in your garage if it's attached to the house. This will cut down on drafts, saves energy and can save you money on your bills.
The Department of Energy estimates that 2 % of all air leakage comes though electrical outlets.
It's easy to do, follow all manufacturers directions even you lady's can do this.
(I learned how to save even more when resurrecting)
You can put safety baby outlet covers on the outlets that are not in use on outside exterior walls, this will help prevent air that leaks in though holes in outlets. Now I have to go out and buy some, so I can save even more money.