A GFCI (ground fault circuit interuptor) can be used in a garage and should be all for the fact that at sometime you will have water on the floor and will plug in a power tool or light. But with lights on seperate circuits you have the option of using all of the lights or just a portion of them. I have twelve incadescents in my garage with the four corner lights being 300w halogens. Sometimes I only need a small amount of light in the garage so the inner banks of lights are on dimmers and I leave the outer banks of lights (halogens off). The safety factor goes up too when lights are switched seperately. If you are out at night working on your ride and you happen to pop a breaker, you still have lights to manuever your way around. Nothing worse than all the lights going out while the tranny and tools are scattered all over the floor and you have to make your way back up to the panel box. But by all means add a GFCI in a garage. A bad shock is not worth it.