As to how useful it could be, I don't know really. I download the "Linking domains" list whenever the total number changes, so that I can see where any new links have come from and what links I may have lost, so for me this additional information isn't really giving me anything extra.
I'm not sure why they didn't just add the date to the existing option rather than having a new, separate one, and in fact am not sure why they added it at all. I haven't read anywhere of people calling for this feature.