SSD definitely is a game changer. I'd wagure that not a single type of hardware upgrade EVER sped up a pc that much as an SSD does it. We got new cpus, more ram, faster graphics cards but the SSD beats them all and if just in terms ot windows speed alone. That alone is worth every penny.
You don't necissarily need one for gaming. You have to wait longer for the game to load but that's it. Some, a very small minority of games, probably benefit from faster loading in the form of streaming details while you walk through a level. But those would probably benefit more from more memory or bigger VRam.
But I suggest to everyone to at least get one for Windows. A 128gb modell should suffice (they come smaller, but those modells below 128gb usually suffer in speed compared to the bigger models).