They aren't essential.
I haven't seen anyone who had issues by NOT having one, myself included. I forgot mine in my high-end rig and couldn't bring myself to rip out the CPU cooler, motherboard etc to install it. Not the slightest problem (Asus Z77 Sabertooth, 16GB DDR3, GTX680).
Not saying there aren't people who don't have issues, just that I haven't observed it.