Well, sometimes when a car goes really, really fast in a straight line on a closed course (some call it "drag racing") sometimes the driver needs an aid to know when the exact right time to shift is, as he has a few things to keep track of, like the direction the car should or shouldn't be heading.
you should get to know your car and how it feels and sounds... my truck (which was my first car and the vehicle i learned to drive stick on) has no tach. and i beleve it taught me to have a feel for the car and when to shift... to this day i never look at my tach on my alti or the 8th gen. idk i would have no use for it.
Say you're building an all-motor K20. It's not that much of a stretch to have a redline at 9500rpm with that square, or even undersquare, motor. If you don't want to run a RSX cluster, or have a massive tach, wouldn't this be the most tasteful option? Have the lights only come on at about 6K and every 1K thereafter?
I think some people's knee-jerk reaction to the words "shift light" may have missed some utility with this thing.