I was just driving my truck to pick up a load of gravel this morning, and on the way checked my tire pressure from the dash readout to make sure I was inflated up for the load. Sure enough, one of the tires that was supposed to be at 40psi was at 27psi. Not enough air down to really stand out (not that I did a walkaround or anything) but way too low to take 1/2 yard of crushed granite.
I would have never caught that without the onboard sensor. It probably happened over the last couple of days. I'm drilling a new ag water well and have been driving up to that parcel a lot over the last couple of days. I share one farm road with my cousin, whose two workers have a habit of thinking they're in Tijuana, where the "garbage can" is wherever you're standing at the time. Big old screw in the tire.
Same technology saved me earlier this year when I got a catastrophic puncture in the desert on my 4Runner. I was on a 4x4 trail, and from the roughness of the trail, would never have noticed if the warning light hadn't come on. That one was bad enough (I could hear the air leaking out and I was in a really bad spot), that if I hadn't had the warning, I wouldn't have had the couple of minutes to get off the steep rock slope I was on and to a relatively safe area for a tire change. Would have likely ruined the rim as well.
Anyway, as much as I sometimes grumble about "new fangled complicated stuff" on new vehicles, I sure am glad for it other times.