this works in such a way, as only heat producing element is those black chips on the stick, so by using these heat spreaders, you actually now transfer heat from black chips to the wider area of metal, thus increasing the heat dissapating capacity. but why you should be needing them? as RAM doesnt gets hot enough to minimize the heat (unless overclocked brutly)
so it wont help much, but sometimes becomes a problem for the user, asmemory slots are too close, that attaching these heat spreaders, you wont be able to insert 2 modules side by side.