Well, because I'm going to buy extra ram, I'll be testing it out, and for example, if it's not in place correctly, a little bit loose, then I would be needed to disassembly my whole laptop once again. But when I stick the correct once in the back which work for sure, than I can, when I buy the extra modules, easily connect them.
And when they don't work I can just get rid of the back and check if they're ok.
Thanks for the reply!