Basically it means that it won't be able to handle higher resolutions as well as the GTX 670 because of the reduced bandwidth.
Because of the 25% reduction in bandwidth, a stock GTX 660 ti performs between 10-20% worse than the GTX 670 in games. (although a overclock can result in it performing just as well as a stock GTX 670)
So far what I've gathered then is on a single monitor 1080p the 680 is overkill, but the 670 is feasible albeit kind of a waste. With that in mind what is the difference between a standard model and a FTW (For the win edition)?