Though 20mm thick gs120 pushes the same airflow as normal 25mm thick fans you can save 5mm space which may matters when you try to add a side panel fan and you already have a tower cpu heatsinkor when your tower cpu heatsink fan slightly blocks your memory slots you definitely need this 5mm space thatacirceurotrades when gs120 is designed for 20mm thickness allows for more space inside your case you can easily mount big and tall heatsink as you want with a 4 pin pwm connector gs