Any memory that's going unused by apps is going to be used by the OS for caching disk contents. That's not as significant with SSD as with rotational drives, but it's still providing a benefit, albeit one with diminishing returns as the size of the cache increases.

That being said, if this is a laptop and if you shut down or hibernate your laptop on a regular basis, then you're going to be flushing the memory cache all the time, and it may buy you less.

IIRC, Apple's default mode of operation on their laptops these days is to just have them sleep, not hibernate, so a Mac user would probably benefit from that cache.