The first benefit is the 99% UV protection. Your dash and the leather/plastic surrounding your instrumentation take a beating from the suns UV rays over time. You will start to see cracking and fading if not protected by these damaging UV rays. Your leather seats will crack and fade as well as fabric seating.
Another great benefit is the heat reduction from tinting your windshield. The majority of the time people just tint the side windows and the back window. Tinting the sides and back cuts down on the heat significantly. But the sun still shines through the largest piece of glass, the windshield adding more heat. These clear films can also reduce IR (infrared) heat caused by the sun as well. Tinting the windshield significantly reduces the heat and makes your car much cooler.
You will also see a major difference in the glare from the sun. We all know how blinding the sun can be when we're driving into a sunrise or a sunset. Window film on your windshield can help reduce this glare and make our driving experience much more tolerable .
Lastly and most importantly skin protection. Our health is the most important of all and tinting our windshield reduces the UV rays from beating down on us. According to the Skin Cancer Foundation, over the past three decades, more people have had skin cancer than all other cancers combined. And each year in the US, nearly 5 million people are treated for skin cancer. In 2006, in the most recent study available, 3.5 million cases were diagnosed in 2.2 million people.