If your tires and under-inflated it can cause flat tires, blowouts, skids, and lengthen the stopping distance of your car. Unfortunately it can be hard to tell when tires are under-inflated because you might not be able to tell until they are seriously under-inflated and the pressure gets below 20lbs.
Modern cars and trucks these days are often equipped with a Tire Pressure Monitoring System (TPMS). This 
technology has been used for years by race car drivers but only recently made its way into the wider commercial world. Race crews use this technology to nip tire pressure problems in the bud by monitoring tire pressure as a car goes around a track.
Of course these TPMS aren’t free. Studies done by the US government estimate how much you can expect a TMPS system to cost; taking in to account the cost of the system itself, keeping the system maintained, replacing broken parts, and other cost increases. These costs are offset because you’ll save money on fuel and tire wear, as well as saving time and money by avoiding property damage or delays to your travel. Altogether the net cost of the system is estimated to be between $27 and $100.
The government also predicts that these TMPS systems can save lives and that it will cost between $3-9 million per life saved. This is an important piece of safety equipment that can prevent you from suffering from the most common vehicle failure and it could mean that you avoid potentially fatal accidents.