I've been using KDE for very long time (except when it lost all of its stability in the beginning of KDE4).
Lately, since everything was going smooth with my NixOS setup, I've decided to remember my good old window manager days and try out some tiling WM options. After all I am already using an extension for KWin to have tiling feature.
After a bit of head scratching and trying to remember the configuration (which is done via lua), I sorted out most of the window management stuff.
Then the reality hit me: The difference between a desktop environment and a window manager. And even after solving some of the problems, I've decided to stay with my cozy KDE. Maybe I am too old to rice now, even with NixOS' declarative configuration which skips most of the hassle for me. Here is the list of functionality I needed to set up manually to get half of the comfort of using a desktop environment:
Networkmanager and secrets
You realize how easy was to connect to a network. Once you set up, it was magically automatic afterwards. Because your desktop environment has a wallet system which allows applications to keep their secrets (like your wifi password). If that's not running, you need to manually configure the network or find an alternate secret-handling mechanism.
Brightness & volume controls
Don't know if I was unlucky or is this common, but I've realized my keyboard shortcuts are not working. I've needed to set up keyboard shortcuts for brightness and volume. Also I set those (with an awesomewm extension) to show it on the tray.
Speaking of trays: LOL. The applications you use and used to minimize to tray (slack, telegram, steam etc.) will be unreachable once you close the window, because there is not system tray (if you don't set one up). Luckily awesome provides a simple systray implementation (which for some reason doesn't always work for all icons but I didn't dig).
I have 2 monitors and a dock to attach my laptop at work. I set up my desktop once with KDE and it knows which monitor is on the right since forever. Have fun scripting around with xrandr and autoloading the correct setup with autorandr on every boot etc.
This is also important: The feeling of completeness on the desktop. Sadly this is not possible with WMs since every small application you use has different design decisions, different shortcuts and feeling. People are trying very hard to theme everything to get this feeling, which is almost same as clicking to "Apply Theme" button on a DE. What can I say is: Good luck!
Yet, I still love the flexibility of tiling window management. I've set my alternative configs and logging in to awesomewm from time to time. Maybe one day..