More memory allows for more programs (multiple tasks) to occur simultaneously, less memory means the programs have to take 'turns' to use that small memory (parking) space to still perform the same job required. So in my case I have my Antivirus running (of course) then the Wireless App, NVidia Experiance, drawing all the icons on my screen etc. all running even if only BF4 is played I was still using 2 or more GB of my ram to just 'work' on the machine. So I made and many people make the same deciision, go 16GB.
If you can do it, it is very helpful, it does give you 'room' to do more (in my case run my own music in the background as I ran BF4,be able to open several webpages to look at hints and tips on websites and youtube, etc.) while I am playing BF4.