What exactly do infusions do?

When you find an infusion, you can choose to use it to improve your health, shield or salts capacity. What exactly do these options do? Will I get more power uses per salt pickup if I improve salts? Will my shield be stronger or regenerate faster, and by how much? How much health will I gain per infusion, and will it make health pickups more effective?

Solution 1:

Infusions level up the health, salts or shield up to level 10 each. They do not add any other qualities besides making your bars bigger so you can take more damage, use more salts and have more shield . You can find vigor boosts that let you for instance use less salts for possession ....

Solution 2:

An infusion increases the size of your bar, though I have not encountered any information suggesting what the actual numeric value is. The benefit is definitely getting "stronger". Shield and Health make you harder to kill. Salt gives you more salt to spend on using Vigors. They do not affect your regen rates or the actual gain from a restorative pickup.