Actually from what I have heard it is not necessary. Unless you oc a lot, ram does not get hot enough to need a heatspreader. In most cases it's a nice cosmetic touch-up.
They do look cool. However, for many the price you pay extra for having a heatspreader is not justified. I really do not mind. I could have bought my ram with a headspreader but the extra price that I had to pay for it was not something I considered important.
If you really want a heatspreader, dont get one that comes on the ram and that costs about $10 more, go to a store or newegg has them for like $4 or something.