I don't think that kind of memory usage is necessarily common - I get sessions that grow for whatever reason but typically I can have several emacs instances running at once using less than 100MB each - the ones I treat like notepads are often less than 10MB.
Hmm, why would one run several emacs instances? Emacs supports the client-server model, which I find very convenient and fast. Basically having `EDITOR="emacsclient -n"` allows you to use the one emacs everywhere.
I run them with different color themes and fonts (randomly chosen from a list on startup) so I can instantly see which window is being used for which project (I juggle several at work - I also take advantage of Windows 10's virtual desktops so get them spread out all over the place). If one of them goes haywire I don't feel bad about killing it since the others remain unaffected, so I never really considered using just a single server instance. Since I don't run out of memory and have CPU cycles to spare most of the time, it works well enough for my current needs.
I also tend to run the windows with partial transparency so I can see bits and pieces of other sessions/browsers/etc behind them - something I was slightly hesitant to start doing but that has made using the computer feel much more "lightweight" (for lack of a better term). I've found it surprisingly useful to have emacs show a second buffer slightly faded directly through the first one.
I too, for a time, had setup my system so that windows were partially transparent. It looked cool, and helped to find windows when they were hidden behind other ones. Then, one day, I turned the partial transparency off, and found it to be very relaxing on my sight and brain. I didn't feel any strain when I started, but I guess it accumulated.
For context, I use a tiling window manager with an average of 4 to 7 windows per workspace-monitor combo. Back then, I also set up a moving background (a screensaver always on in the root window). In fact, I think that was the primary motivator. I had gone years without a wallpaper because having a tiling window manager made it meaningless and I was missing having some eye candy. Having partial transparency would let me see the moving background through the windows. Anyway, I digress and I'm back to no transparency, no background, in any case.
