You've probably either owned a car with a hard-to-open hood or at least known someone who's had to deal with it. While it won't directly affect the vehicle's operation, a hood with a tricky latch or one that won't open at all can be extraordinarily frustrating when you need to check something in the engine. On the other hand, a hood latch that doesn't hold things in place can be dangerous, especially if the wind catches the hood while you're driving.
Latches will vary between different makes and models, but they are typically constructed in a similar manner. Most involve a swinging hook on either the car body or the hood panel that latches onto a grab bar or into a fitted slot to keep the hood in place against the car. If this mechanism rusts, it may be difficult to get it to move, but you can usually clean it off and add a touch of grease to get things moving again.
If the latch is broken or damaged in such a way that it is basically ineffective, whether it won't latch properly or is difficult to open, you'll probably need to replace the mechanism. That, or you can always learn how to jimmy the latch every time you want to take a peek under the hood. Since you need to monitor fluid levels and perform regular maintenance, leaving the hook damaged can get pretty aggravating after a while.
So what happens if you want to replace the latch, but damage to the car makes this a near-impossible task? This is where handy devices called hood pins come in. They were first developed as an alternative to the hood latch for race cars, as the pins are more lightweight than traditional latches. Typically they are used on custom vehicles, since they allow fast access to the engine, but they can be a good alternative to repairing a broken hood latch in some cases.
The pins are mounted to the core support that is also responsible for holding up the headlights and the radiator. They're usually placed at the front end of the hood where there is about two inches of depth below the hood for the device. If you decide to go this route, you'll need to drill holes through the vehicle's hood.