I might have already replied to this thread and mentioned this before, but I had a factory TPMS on my BMW and it was really a great system. It was able to compensate for changes in ambient pressure in order to display the nominal tire pressure regardless of whether or not the tire was hot or cold. Without the temperature compensation, of course what you'd see on the display would be rising pressure as the tires warmed up from riding. The practical implication is that you could keep an eye on the tire pressures in real time, which was a benefit when touring. It saved you the trouble of needing to check your tire pressure in the morning, so that was one less thing you had to do to get under way on your trip.
The other thing the system did was take the accuracy of your tire gauge out of the equation. You could use any tire gauge, even an inaccurate one, and set your tire pressure correctly. Procedure: note the tire pressure reading on display. Let's say it was two 3 PSI or 0,2 bar low. Then you measured the pressure with the tire gauge. Regardless of the reading, you add air until the tire gauge indicates you have added 3 PSI or 0,2 bar. Now, when you get back on the bike and ride it, the pressure will indicate nominal. Perfect.
The only downside of the system was you had to ride the bike to wake up the sensors. So, if the bike had been sitting for a while - say in the winter - you had to either just ballpark it with your tire gauge to be safe, or else take the bike for a quick spin up and down the block to activate the readings.
Now that that bike has been sold, I kinda have to agree with you, ferret. Although the BMW TPMS was nice and I used it, it's not essential. Getting by with a decent tire gauge and being observant also works perfectly and isn't really any hassle.