If you need the extra ram it is not a bad idea. If you had no ram and wanted 12GB I would have recommended 3 x 4GB because of efficiency and leaving further upgrades open.
I was also thinking about getting 3 X 4GB but Asus didn't have such a kit in their approved/verified RAM list -- I was nervous about doing that since this was my first build attempt in 8 years. Oh well.
You mentioned efficiency -- is it because having the same amount of RAM in fewer modules is always faster overall? Or is it just a matter of taking up less slots and having more upgrade options for the future?