I'm not so sure if what I am about to say is all correct but my experience with RAM optimizing applications is that they could / might potentially be beneficial for users with limited RAM under certain scenarios. There is however a bit of a downside too.
When using your computer you sometimes get memory leaks, programs not clearing every ounce of RAM they should / could, residual stuff... In those cases I guess potentially a RAM optimizer would help because as far as I understand it the thing just clears RAM unassigned parts and repopulates them with stuff that is necessary (or leaves it blank).
From my experience however that comes with a drawback as it also purges stuff that is cached / waiting to be used. I tried a few of these back in the early 00's and stuff like games actually needed more time to load, cache everything from disk onto RAM and all that. That in turn made the process of starting up a game longer but I guess once you were in the game and once RAM got populated with info again, you gained those few MBs (back then 128mb were bragging rights) that made the HDD scratch a little less...
But yeah, do take what I said with a grain of salt as this was way back and I might be remembering it wrong. What I do remember is that overall I wasn't that impressed and disk spinning was higher than it normally was when starting applications.
In rendering, I suppose that would help. If you can clear 1gb of stuff then thats dandy. Overall though you gain much more speed by just simply upgrading RAM (quantity wise, not speed). Don't we all just LOL when you click a button (say, chamfer) and then stuff gets loaded from your SSD / HDD and you sit there for 5 seconds wondering whats up with that? Because I fear that is sort of what can happen with RAM optimizers... :P