You want to buy a headlamp because of its advantages over flashlights, a lantern or using a flashlight app on your cell phone.
Here are 4 main advantages:
1 – Hands-free
the ability to use both hands is a major advantage over a flashlight, and for certain activities like climbing, hands-free is an imperative. Even around the campsite where a lantern can provide general hands-free lighting, the ability to easily direct extra light wherever you’d like, with just a nod of your head, is an advantage
2 – Beam Distance
most of the lights over $30 offer a spotlight mode capable of casting an impressively long beam. This can be a big asset for finding things in the dark, such as the poorly marked trail back to your car or campsite.
3 – Durability
many of the higher quality lights are built tough, offering water resistance sufficient to operate in sustained rain storms (IPX-4), and some are waterproof to one meter depth (IPX-7). This makes them particularly attractive for those going into the backcountry where weather tends to be unpredictable.
4 – Compact and Lightweight
they are easy to fit in your pack, and the more lightweight the better.