Yes, they do help, not even the gamers, but anyone else too. You need to use at least 2-3 fans inside the computer case in order to provide a steady flow of new, cooled air so that the motherboard, CPU and video card can run at lower temps.
In the video from above you will notice that when you do not use case fans the temps are as following CPU @ 71 degrees C, GPU @ 92 degrees C.
With 1 front + 1 back, you already win a lot: CPU 61deg + GPU 79.
With 2 front + 1 back + top, you win more: CPU 55deg + GPU 76.
After a while you can as many fans as you wish, but the effect won’t be noticeable.
The sweet spot seems to be when using at least two fans. Make sure you use case fans, people!