I believe for GC3 it won't be a big deal, but you definitely want to use SSD's for most gaming.
When I play Total War: Warhammer with my brother, it takes forever. He's running on a notebook drive, I've got mine on a slow SSD, my map loads take a few seconds, his go about two minutes. Our systems are actually close to the same age, his actual processing power isn't that far behind, but the dogshit drive makes for obscenely slow loading times. Unlike GC3, these load times occur twice any time you manually fight a battle. I've got a 2400MB/s drive in my laptop(which he refuses to use to play...) that basically removes waiting for load screens from the equation entirely.
Games are getting pretty damn big, so any of them that have frequent in game loading are really going to drag on you when your drive is only doing 70MB/s.