Anti-aliasing in games and its relation with VRAM

I know the fact that Anti-aliasing is a very heavy process in games and slows down the game play even on strong hardware but I want to understand it more in order to make the best choice in graphic settings in games.

I've read here http://www.tweaktown.com/tweakipedia/89/much-vram-need-1080p-1440p-4k/index.html that games like GTA V can take up to 4GB of VRAM on 1080p resolution. but tuing on the AA option increases the amount, maybe up to 5GB VRAM. I have AMD Radeon R9 390X with 8GB VRAM. I've tested it with this game and watched the VRAM usage using monitoring programs like Afterbuer but none of them could still answer my question.

is AA something to depend mostly on the available VRAM and not the GPU cores? the games uses half the VRAM, (I can tu on frame scaling and let the game even use all 8GB of VRAM), I waa know if I tu on AA will it only use the free VRAM or it will put extra load on the GPU too and as a result slow down the game and lower overal FPS? thanks! I'm using latest AMD Radeon driver and Windows 10 X64