I think the most I've actually used at once is about 20GB, I have 32 on my PC and typically don't use over 10GB or so unless I'm really trying to, with both monitors open. I think this was a combination of coding projects, Skype, browser, and maybe doing some graphic design in GIMP. Windows 10 generally eats up a few GB on its own but with 32GB it's nothing significant. I've had a full screen game running along with 3 streams at once on my second monitor and some minor background stuff, I think it still capped at 14GB or so.
Spoiler
-This isn't counting artificial benchmarks or the like.
-I don't use Chrome and don't keep billions of tabs open at once. I actually prefer to keep my browsing on my laptop so I can reference it on the side without taking up screen space and further control my audio levels. I'm sure many folks do something similar with their phones, but my laptop only has 4GB of RAM as it's ancient so even combining both systems it doesn't change my peak numbers much.
-I don't really do video editing or 3D modeling, which can easily bloat the system's memory budget. I also do run games in 1440p generally, and have a 4k second monitor but it's in portrait mode so therefore I don't run any 4k content as a rule. I suspect running a browser preferring higher resolution content probably also skyrockets certain resources but for me unless I'm watching a stream or video in full screen it's usually pretty low res. After all I consider it fairly pointless to watch a stream of a 20 year old game above 720p which is a large portion of my content consumption.
-Any coding I do is strictly nothing fancy, though some projects can run fairly large my average use case is not heavy duty as Sharpeye alluded to.
In fact it's possible to overrun your physical RAM in some cases, though virtual memory will be terribly slow since it generally has to read portions in and out any time you change tasks. Not every OS will handle this well and it borders on unusable in some cases. My laptop uses OSX and only 4GB RAM, and I can easily go over that if I'm running anything demanding alongside a browser. When I switch apps it will generally take a decent amount of time to shuffle everything around and make the new app usable. As long as I'm just sticking with a browser on this machine and not multitasking I still can effectively use the whole memory capacity on that application and it runs fine.
Although many of us may not go over half usage with 32GB it is more optimal than 16 for the following reasons:
-The OS and background tasks will take up a few GB at all times. W10 is especially annoying about resource management and is very defiant to your attempts at productivity with self updates and the like. For me right now it's about 5-6GB with nothing open. If you only have 16 measly GB then upwards of 30% of your memory will likely be dead at all times, perhaps more. With 32GB+ you have more than double the usable budget, roughly 10GB vs 26GB in practice.
-Future proofing. Not only will the OS only continue to bloat to ensure planned obselescence and the sales of future generations of hardware, but every other application and the content itself is going to grow in a couple years. The 16GB will hit a hard ceiling quickly; that 5-6 GB being used on the OS could quickly become 8-10 without most users even noticing. Plus as more users are dealing with higher res content it will use a much bigger slice of memory.
-Hitting the max CPU or GPU usage is considered pretty normal under some use cases like gaming that are designed to make full use of resources. If you max out your memory you'll have to rely on virtual memory which is a bad time as I mentioned above. When buying a system, it's fine to buy a CPU or GPU equal to your needs, even if there's no headroom or it may fade in a couple years; at least you'll get the performance you reasonably expect. If you buy memory equal to what you use, you'll be fucked. It's the same mistake as purchasing a pool or bathtub exactly equal to your body's volume.
-RAM is generally very cheap right now compared to a few years ago, 32GB decent speed kits are available from 120$ at a glance on Newegg. You can still overbuy by getting overpriced RGB laden modules or trying to get super high speeds which generally come with a disproportionate increase in price for the modest advantages, but getting double the amount you expect to use is really not that bad from a price standpoint. It's not like the 60$ difference will let you upgrade to a 3080 GPU or something.