Comment by HeyLaughingBoy

It usually is. I try to think of these things not as "waste" but as "cost." As in, what does it cost vs. the alternative? You're using 40Gb of some kind of storage. Let's say it's reasonably possible to reduce that to 20Gb. What's the cost of doing so compared to the status quo? That memory reduction effort, both the initial effort, and the ongoing maintenance, isn't free. Unless it costs a lot less to do that than to continue using more memory, we should probably continue to use the memory.

Yeah, there may be other benefits, but as a first order of approximation, that works. And you'll usually find that it's cheaper to just use more memory.