Dont understand the question. Do you mean if its recommanded to have more than 8GB for gaming?
The games are programmed that they dont use all the free RAM completly, because there have to be some space left for the system. The more RAM you have, the more RAM will get used by the game. I personally get 10 GB+ RAM consumption by some new and high quality graphic games.
It may be that it slows you down, if you dont have enough RAM, but it is also possible that things, that are not very important for the Programm (i.e. a game) performance gets loaded in the RAM. Its a matter of programm designing. But in general, I would say there are some performance gains, when using much memory capacity.