Should I buy low-profile RAM for big coolers?

Yes, if your cooler overhangs the RAM slots. Standard-height RAM will hit the bottom of a big air cooler, forcing you to raise the fan and hurting cooling. Low-profile RAM is a few millimeters shorter and costs only $10–$20 more, saving you a return headache or a worse-running PC. Check your cooler’s clearance spec first—if it says “max RAM height 32mm” and your RAM is 45mm, you need low-profile.