A hardware radio switch has security benefits to it in that when it is off, you know for a fact that nothing is connected to your laptop wirelessly. The radio switch usually turns off all wireless communication, including Bluetooth and 3G.
I have heard that this is a requirement in certain military environments, but I have not seen any evidence that this drove the development of the feature on any laptops.
The physical button is not just to disable the wifi, but it should actually power off the device hardware.
When you disable wifi in your settings, the device is still powered up and using some power. It may not be a lot of power, but when you are commuting, every little bit helps. If you really want to save maximum battery life, then you want it to be consuming zero power.
Not for aircraft safety
Contrary to a commonly held belief, it is not for travel on aircraft. The FAA regulations apply only during takeoff and landing (and even those are currently being reconsidered). If this were a requirement for safety, every device allowed on an aircraft would have to have a hardware button – including mobile phones, tablets, and ebook readers.
Additionally, the rules for takeoff and landing specify that the devices themselves have to be turned off, not that the transmitters have to be turned off. So a switch would not comply with the current FAA rules on takeoff and landing.
Update: An FAA safety panel have just ruled that Wi-Fi is safe to use on airplanes, and the changes will likely be adopted soon. This just goes to show that it has nothing to do with safety, and never did.
Source: I am an electronic engineer with specialist courses in communication and wireless transmission. I have also taken a graduate level course in safety and security specifically in air transportation.
Besides the arguments others have listed (Aircraft requirements, power saving) we should not forget about security.
Before the tablet and smartphone era you had a great control over your computer in an emergency: if you pulled the UTP cable, you could guarantee that the computer is isolated from the network. If you pulled the power cord, you could guarantee that your computer is turned off.
With all these physical controls removed we arrive to a situation, where in case of a malware or hacking attack you have no option to stop your device from being remote controlled by the attacker, besides removing the battery (or smashing your device apart with a hammer if the battery is not removable).
With everything controlled by software, how can you be sure of your connection status? You might think you disabled wifi, but if your system is compromised, it can exchange data without you knowing it, while displaying that it’s turned off. (Even if you turn your device off, it might just simulate it and darken the screen, and still run in the background.)
You might personally like thin clients and you might personally trust your software 100%, but there are people who don’t, so why remove this option from them?
These switches allow you to disable wireless transmitters without first turning them on in the middle of a flight, when their use may be prohibited.
There seems to be some consternation regarding this answer. I have reworded it to address some of the concerns that have been voiced. In addition…
- I’m not saying that any rules regarding the use of wireless devices during flight are justified, only that they exist.
- I’m not saying that any specific organization (such as the FAA) has made rules regarding the use of wireless devices during flight, only that some organizations (perhaps individual airlines) have put them in place and that they affect a significant number of air travelers.
- I do not mean to suggest that this use case is the original or only reason for these switches, only that it is a valid use case.