I agree that a lot of it, we could do without, but yesterday the tyre pressure monitor paid for itself.
I left home, tyres were fine, then I checked the pressure after about 10 minutes (while riding), and the rear had dropped 0.5 bar. When I stopped at a petrol station, there was a nail in the tyre. I was able to pump it up, and limp on, keeping an eye on the pressure. We then plugged the tyre, and I was able to keep an eye on the pressure afterwards, without stopping every 5 minutes to make sure it hadn't gone down.
Now, I'm sure that bods have, and will cope without this witchcraft, but yesterday, it was a godsend.