said by cdru:My new house came with just a steel door. First winter I had no insulation on it. That summer I insulated it and I can confirm and agree it helps keep the garage somewhat warmer in the winters than without. At least all or most of the snow melts off the cars now.
When I replaced my garage door several years ago, the readily available options were either steel tray with no insulation, steel tray with styrofoam insulation glued on the back, or insulation sandwiched between two steel panels. I went with the latter as I didn't want just a steel tray due to noise, and with multiple kids I wasn't sure how long the styrofoam insulation would last.
Like Viper above, I have a noticeable temperature difference between inside and out of my garage in winter. Any insulation is not going to hurt you aside from initial cost.