You'll still get an increase in the number of things you can have loaded into RAM at once that's proportional to the reduction. That'll give you far more leeway in when trying to load resources on the fly, which most games still struggle with. So reducing memory usage is definitely something you want to do regardless of how much you have.

Also, if it's a PC game, you're looking at memory limits far below what the HW may offer - at least if you want it to run without annoyances. Windows limits the amount of memory it'll allow to be committed to the DRAM size + (current) pagefile size (may only be 4-8GB on SSDs); note how that doesn't include GPU memory - and allocating that counts as commit due to how residency works. Then you're looking at the OS eating 2-3GB of that, plus 1+GB if the user has a browser opened, plus anything slowly leaking memory. And a LOT of recent Windows applications leak memory or actually use insane amounts (including, amazingly, a built-in service on Win10) - if they never access it again it'll eventually get evicted from the working set, which means it only counts towards committed memory; task manager doesn't display per-process committed memory by default. That's only a fraction of all the problems.