What is armour for? In battle, its job is to protect the wearer against the most common dangerous attacks. Which leads to some general principles:

1. Helmets are very important. You can get a lot of protection by using a shield, but if you want to see what is going on, you need to look over the top of it, which will expose your head. Attacks to the head are also very dangerous, so protection is important from that perspective, too. For minimal armour (which could consist of as little as shield and helmet), the most important piece of armour you wear is your helmet. Face protection is nice, but it's also nice to be have good vision, to be able to breathe easily, to be able to eat and drink without having to take your helmet off. An open-faced helmet (perhaps with minimal face protection such as a nasal) can be a suitable choice.

2. Some very common and dangerous attacks are arrows and spear thrusts. These attacks tend to be aimed at the torso. Penetrating wounds to the chest or abdomen are very dangerous, and torso armour is the next most important thing to add after the helmet. To do its job of stopping arrows and spears, it needs to be thick enough to stop arrows and spears, and provide enough coverage to be useful.

3. Arm and leg armour can be useful. However, the arms and legs are where you want to carry the least weight, because you move them more/further/faster than your head and torso. It might not be possible to provide reliable protection against arrows for your limbs without excessive weight. In this case, there are a number of possible choices:

• Wear no limb armour. This is the lightest but least protective choice. You are much more likely to survive an arrow to your knee, a spear thrust to the arm, a sword cut to your forearm, etc., than an arrow in the chest or a sword cut that penetrates your skull.

• Wear limb armour that provides the best protection against arrows that you can manage for the weight you are willing to deal with. For example, you might wear plate arm armour 0.8-1mm thick. The curvature will mean that most arrows will hit at angles, and will hopefully glance off. An arrow hitting square-on at short range might penetrate. Again, such a wound will be much dangerous than a penetrating wound to the torso.

• Accept that your limb armour won't give adequate protection against arrows, and protect against other dangerous attacks. An amputating cut to a limb is dangerous and results in permanent disability. Thus, one might wear limb armour that protects against amputating cuts, even if it provides minimal protection against arrows (and various thrusting attacks). If such limb armour is sufficient light, this can be a good choice. (If you could wear plate arms that give protection against arrows through curvature/angle for the same weight, the non-arrow-protecting arm armour might be a poor choice in comparison.)

(Of course, as general principles, it's easy to find examples which violate one or more of them.)

Which brings us to splint armour:

It looks like it could only protect against some kinds of attack, being made of metal strips with quite some distance between one another

In particular, it provides poor protection against arrows and thrusts. Where do we find splint armour most commonly? On the limbs, often forearms and shins, where it's even more important to minimise the weight than on the upper arms or thighs.

Note the orientation of the splints along the limb:

https://en.wikipedia.org/wiki/File:Suneate.JPG

This is armour designed to (a) stop amputating cuts, and (b) be as light as possible while achieving that.

An even lighter version is jack chains, which only protects against cuts from the outside.