I added that feature when I wired my Camaro a few years ago. Of course, without the water pump to circulate water, it really was pointless. I never used it other than to occasionally make sure it worked. While it never happened, it could also be a good way to end up with a dead battery.
Fast forward to the past two weeks as I'm wiring the fans in my 70. What I really missed when I was driving my camaro, was a way to turn the fans OFF when the car was riding between the thermostat and I was on the highway. In other words, my fans come on at 190, and go back off at 180. If I'm driving down the highway with lots of air flow, and the car is running 185, if the fans had come on for some reason, they would never turn off. So this time, I wired a switch to interrupt the ground signal from the temp sensor in the head, so I can turn the fans off, even if the sensor is calling for fan. I also wired in a manual switch, but it requires the ignition switched 12 v.
NOW that said, if you go that way, make SURE if you use this switch you understand that you have to MANUALLY turn it back off to get cooling fans! When you get off the freeway, you better remember to turn them back on, otherwise, you're not going to be in a good mood when you get home!!! This approach may not be good for everyone.