With SMS Relay, I really don't need a blinking light anymore. Notifications happen on both my phone and my MacBook, so if I miss it for some reason, then something is seriously wrong.
I don't doubt that the notification light is something that you would use. Just not all that important to me at this time.
If my phone is charging upstairs I can be down stairs with my iPad and not worry about I coming.
The notification light supporters have only one circumstance I can see that it is useful. In a dark noisy bar where you are actually holding or looking at your phone instead of being in your pocket. Even then I can use the light assist to do the same thing.