Empty ram is wasted space. its not helping, its not making PC any faster, if anything the less that is cached is just more you have to load when it comes time to running something.
Windows memory management tries to operate PC in such a way it is most efficient. Its not efficient to close programs, write all the data to storage and then if you open program again, reload it to ram... no, its more efficient to compress that data in ram and if you open program again it only has to decompress it which takes less time. There is more to it than that.
Windows 10 will shrink and grown depending on your ram amount. win 10 can run in less ram than all previous versions of windows until you reach windows xp. It just uses more page file as it shrinks in ram.
I can't say much as I have 8gb free ram right now and 13gb in standby so my system has more than I use too. I don't know why I have 13gb cached, it seems a little much for what i do.