
Take a look at this benchmark from Linus Tech Tips:

Each frame might only have a few milliseconds to process a lot of data, so if the game you’re playing is CPU bound (like CSGO), faster RAM can improve framerates. In games though, RAM speed can actually have a noticeable effect. In day-to-day tasks, the RAM being a few nanoseconds faster might not matter, but if you’re really crunching numbers, any small performance improvement can help. Improving the speed at which your RAM runs can directly improve your CPU’s performance in certain situations, though there is a point of diminishing returns when the CPU simply can’t churn through more memory fast enough. Once it’s loaded, it usually stays there for a while, being accessed by the CPU whenever it needs it.

Every program you run gets loaded into RAM from your SSD or hard drive, which are comparatively much slower.
