I should know this for sure since I have a fairly high spec(12 core, 32gb RAM) system that runs SL as its primary OS(legacy applications), but AFAIK all versions of OS X have pretty much expanded to fill available RAM given enough time to do so and put it to use.
This was not the case in the "classic" OS. I have computers like a PowerMac 9600 that have a ludicrous amount of RAM given their other specs(1.5gb in the 9600-12x 128mb modules) and I've never even come close to filling up the RAM on them. I can do it in OS 9 on something like a G4 where I might be handling big image files(film scans) in the scanner software or Photoshop, but the 9600 is too slow in other area to reasonably consider it.
In any case, from what I know of *nix OSs(most of my experience with them is OS X/macOS, but I also have some experience with IRIX and a bit with Solaris), the general philosophy is "unused RAM is wasted RAM" and "find something to do with anything not actively in use." This was a bit jarring when I switched from Windows 7 to OS X 10.7(the current versions of each when I made the switch) but ultimately I came to appreciate it. Back in the 10.7 days, I would look at my page in/page out ratio, and specifically the number of page outs, to see if I needed more RAM. My first Mac, a late 2011 13", shipped with 4gb, and I would routinely see about as many page outs as page ins. I upped it to 8gb, and for a while I'd see a few thousand page outs for every million page ins, although this crept up over time. Now on a 2012 MBP with 16gb of RAM, I'm currently at 45K outs for 7.3 million ins-still not a ratio that concerns me too much.
10.9(Mavericks), though, did do a few things with memory handling that were ultimately for the better, although initially I was resistant to them(as I think were a lot of people). On the handling side, it introduced memory compression, which is a concept I admit to still not fully grasping, although it's there and works. The bigger change for the end user, though, was replacing the pie chart of memory usage with the "memory pressure" graph. I think for the average user, and even the moderately technically minded one, it's not abundantly clear what the different between, for example "active" and "wired" memory is, and how "inactive" memory differs from "free" memory. BTW, on my MBP that I'm typing this from, only 24mb out of 16gb is claimed as "free" although it also only claims 7.92gb as "used" leaving over 8gb that the OS is apparently using in some capacity(3gb is claimed as swap, for example).
In general, I don't like Apple seemingly "dumbing down" features in the OS, but given how complicated memory management actually is in OS X I think that memory pressure is actually quite a useful indicator. Basically, as long as it stays green, you're fine. Occasionally flirting with yellow is fine too, although back in the fondly remembered days of user upgradeable RAM on most of the line up, frequent trips into yellow meant that you should be shopping for a RAM upgrade. When it hits red, you can either figure out what's eating up your RAM and kill it, or just let whatever it is finish what it's doing.
I've only routinely seen pressures in red on computers with 2gb of RAM. Most notable among these is the 2009 MBA, which of course is stuck there. I recall installing the Sierra Beta on a recently acquired unibody(white) MacBook which-at the time-still had the 2gb of RAM it came with from the factory. I visited the Apple store a day or two after installing to try and get a replacement rubber bottom(I'd apparently missed the cut-off on free replacements by a few months). The Genius who waited on me hadn't played with Sierra yet when I brought it in, and I told him he was welcome to try, but we both agreed that first beta with 2gb of RAM was unusable.
