Besides being an indicator of inefficiency, RAM uses a lot of power. In the region of 10-20% of overall system power. That's not even factoring swap space into account, which is a greater burden on power.

It's a sign of bad resource management. Why does whatsapp need 600mb if a native messaging app uses fraction of that? Why does atom/vscode (electron apps) need to use gigabytes of memory, when I can open two orders of magnitude larger files in a native app with two orders of magnitude lower memory consumption?