The biggest issue is probably the DUST. Chickens generate lots and lots of fine pale greasy dust, especially when they are molting (which they do several times between chickhood and adulthood, and then every year or so thereafter) but some is produced all the time. So it depends how you'd feel about loads of greasy dust all over your garage stuff. (To some degree you can minimize the problem by having solid walls on the coop, but you still need ventilation and for parts of the year you will want at least some of that ventilation to open into the garage)
Light-wise, the best arrangement is to utilize an existing garage window. The coop's interior wall(s) can have a big transparent window-style panel to let the light continue onward to the rest of the garage, so you are not totally blocking off the window. Or, cut a new window. In principle you could use electric lights instead, BUT then your chickens will be in pitch darkness anytime the electricity is out, and at night (unless you use a nightlight, in which case see above re: electricity going out). At the very least, make a clear popdoor so they get SOME outdoor light. In fact, since you'll be cutting a hole in the garage wall for the popdoor, you can cut it extra big and just make a large transom-type window atop it, that way you get both things from just one hole in the wall.
Another limitation is that you have to have room for the run to be attached to the garage -- for some people this works fine, for othres, not, in which case the garage is not going to be a good place for the coop.
On the whole, as long as you don't have anything stored in the garage that the chickens will bother (e.g. lots of power tools or an antique car, that you don't want all dusty) and nothing stored in the garage that will bother the chickens (e.g. fertilizers or pesticides with nasty fumes), and don't mind the likelihood of more mice than usual, a garage can work out really well, especially in a very cold-winter climate where it gives you considerable benefits in terms of warmth and convenience.
Good luck, have fun,
Pat