Why <120mm fan / high vs. low pressure?

[AC]

When would you use less than a 120mm fan when it moves the greatest amount of air with the least noise?

Is it better to have high or low pressure in the case in terms of cooling benefits?

 

[AC]

anyone have opinions?

 

[dadx2mj]

I beleive it should be balanced equal coming in as going out next best would be more exhaust than intake get the hot air out