being in an extended period of un(der)employment, i've had some time
to reevaluate my personal system. since i moved to linux, i've used
kde as a desktop, which is something of a behemoth. the metapackage
debian uses in its installer comes with a lot of crap i don't need. 
some of this is inoffensive---i rarely use a disk-burning utility
these days, but it's nice to have one on hand---but parts of it
cause problems. the suite of mail and address book applications that
kde-standard bundles, even for users (like me) who never open them,
keep an akonadi server running constantly in the background, which
can eat up half a gig of ram at idle. this is obnoxious, and it has
to be disabled through your config files despite far more useful and
integral subsystems like kwallet having gui options to disable them.

i like the look, feel, and configurability of kde, but i've noticed
more and more how little of its bundled software i actually use, and
what i do use, i use because it's /there/, not necessarily because
it's the best option. okular, the bundled pdf reader, has good mark-
up features but lacks the ability to handle editable pdfs, which
alternatives like evince have. konsole is a very usable and user-
friendly terminal emulator, but it's enormous, and even a barebones
solution like st doesn't take long to set up with all the features
that i actually need patched in. there's nothing terribly special
about the gui file manager or image viewer; depending on the task, i
already used emacs or vim in lieu of the bundled text editor(s); and
i used vlc in place of the bundled audio and video players. i tried
out lxqt and xfce, and they improved on background resource usage,
but they also just introduced other software i didn't use. so in an
effort to see what i actually used the desktop environment for, i've
been trying a window manager in its place. i went with i3 because it
seems to strike a good balance of lightweight and flexibility---it's
not as spartan or as elegant as something like openbox or dwm, but
it's more easily customizable and its central metaphors click better
with how i use a computer.

the dropoff in resource use is obvious immediately, but i'm running
a relatively new laptop (it's only six years old!), which has quite
a bit of cpu headroom and 16gb of ram, so going from using 3-4gb to
1-2gb in ordinary usage does not make a big difference. it does seem
like an i3 session extends battery life a little over plasma. in any
case, it's largely academic. the value (and inconvenience) of using
a window manager by itself comes down to picking and choosing your
system programs, a process which, if you're like me and have always
used a certain desktop environment, will clarify what a desktop
environment actually does.

some things i had to sort out right away:

* an i3 session didn't automatically connect to wifi, so i initially
  had to connect manually with nmtui. the config file revealed that
  the issue was i3 by default expects nm-applet, a gtk application
  that, coming from kde, i did not have installed. this is a quick
  fix---either install nm-applet or direct i3 to the network-manager
  frontend of your choice.
* i assign ctrl to caps lock and compose to my media key, but in the
  past i'd done this through the kde settings. this stored my key
  mappings in kde's configs rather than xorg, so i had to add "ctrl:
  nocaps" and "compose:media" to XKBOPTIONS. this sets keymappings
  for all x sessions system-wide, which is what i want.
* adjusting display brightness was something i didn't expect to have
  to reconfigure. i3 specifies volume hotkeys by default, but not
  display brightness for some reason, so i had to add those myself.
  most hardware toggles (wifi, microphone, bluetooth) continue to
  work as expected.

less urgent things the desktop environment takes care of:

* "desktop" wallpapers: a window manager doesn't have a desktop,
  strictly speaking, so you need to use a separate utility for wall-
  papers. i use nitrogen---the debian wiki recommends a cute little
  feh script to cycle through your Wallpapers folder randomly.
* the screenshot utility is one of those things i never think about 
  until i need it. in addition to the obvious desktop applications
  that come with any environment---document and image viewers, gui
  file managers---there are a bunch of little things like this that
  have come up in the course of trialing a wm alone. i bind my print
  screen key to scrot -s.
* running flatpak and some local installations requires symlinks---
  otherwise dmenu does not know they exist.
* some default applications i needed to respecify in mimeapps.list.

for the most part, though, going window manager-only was painless.
the lesson, unsurprisingly, is that if you're willing to expend a
little effort setting up a window manager, you can arrive at a point
of equivalent functionality to a desktop environment pretty quickly,
with significantly less resource usage and bloat.