They are what I see as a luxury item. You don't need them but they are NICE to have. Very nice. I built my boss a pc 2 months ago with 2 vertex turbos as I mentioned above. While it's not as fast as 3 vertex turbos, everything is noticeably faster that when he went 2 days for a rebuild for watercooling I did, he missed the instant feel of it greatly. But don't take my word for it the screenshot is the proof in the pudding, which is the benchmark for access times, throughput and cpu usage speaks for itself.
Also to mention, boss has a high end system with 980x just like you Mael. For $120 * 3 it was basically nothing to eliminate the i/o bottleneck and nearly reach the theoretical limit on the onboard controller.
SSD ftw imo. I was going to acquire my first one today, but I ended up buying a G19 keyboard instead. :( Oh well I suck.