the fans help in the cooling ... cost as much as normal fans w/o LED well, there are many things in life you buy which are WANTS and not NEEDS ...
The lights also generate heat, which makes your case hotter, and your fans with the LEDs are not the same quality as the fans are without the LEDs, so it heats your case more, ando nly build over time.
i have a blue fan on the side. just makes it look good and on the front of mine is 2 long lights that change multi coloured. looks cool
My beau's computer has blue lights; it's pretty and is kinda like a nightlight in the dark if it's on. lol