It just ferments more slowly. It doesn't tend to generate any off flavors from being too cold.
If it's cold enough and/or the beer is high enough gravity, the yeast may not be vigorous enough to finish the fermentation. But generally it's just slower. All of my beers are fermented cold in the winter. No harm done. Yeast is really very flexible.
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit