While uses for Positive, Neutral, or Negative air pressure are debated, one thing is certain. Each type of pressure is useful in it's own way. Certain environments and case types can dictate what kind of pressure you are going to use. We will discuss in this guide what is each type of pressure, how to achieve it, and case uses for which is best in which scenario.
Air pressure is determined primarily by which way the fans are oriented in the case. Each pressure type has specific needs that when met create a different cooling environment. The other determining factor is the case take you would use.
Positive Air Pressure
This refers to having the net total airflow in the case be more intake. A good example of this would be if you had seven of the same fans. The setup would be: three fans in the front and rear fan as intake, and the top three fans as exhaust. Without anything blocking it (a radiator would clearly impede airflow, thus needing additional consideration), this would create positive pressure. This is useful for very dusty environments because all air gets filtered. This creates pressure on the inside of the case, and since it is cool air coming in the components can keep cool. The drawback to this is airflow is nullified and if you have components that rely on it, cooling will be more difficult.
Negative Air Pressure
This refers to having the net total airflow in the case be more exhaust. A good example of this is if you have 4 or more fans oriented as exhaust pushing all the air out of the case. In this scenario, the air pressure in the case is negative and removes all hot air, but doesn't reliably bring in cold air. If you are already in a cold air environment and dust isn't a problem, this can be useful for things with passive cooling or hardware that doesn't generate a lot of heat and is generally considered the quieter solution.
Neutral Air Pressure
This refers to having the net total air flow in the case be more neutral. A good example of this is when you have a few fans in the front, and a fan in the back as well as couple of fans on the top. This is the most commonly used setup as it is the most versatile and applicable in most environments. In this scenario, the air is pulled into the case, typically from the front, and then pulled across the components by the exhaust which pulls the hot air out, usually through the top or back. You will want to use the same CFM fans to create this environment because higher-speed fans on one end of the other, will tip the scale in favor of the other which creates an unbalanced air pressure.
It is important to note that, these scenarios are mostly important with more exotic PC setups/environments. If you have a situation where you are using a more cramped environment or an open-frame environment this information would be most useful. Although none of these styles of cooling have negative side effects that harm the system, these are options that are presented to maximize cooling efficiency.