The purpose of those lights was to give a glimpse of the status of the machine - which cores were idling and which were not. The upper 16 LEDs of each board were doubled. I assume the extra ones were used for diagnostics.

If your computer lives in a datacenter, far from view, there is little purpose on them. If, however, it's a smaller unit that lives on a desk or in an office, being able to quickly tell its state is interesting. Good visualization is an art.

Not in person. I don’t see any blinken lights. Water cooled rigs and case lights don’t count.