I've used dwm as my window manager for a couple years now, after switching from i3, and have never looked back (i3 was fine, but it had a bug that was affecting me too often--I don't even remember what now).
For me, the killer feature (aside from tiling vs overlapping) is that on my three monitors, I can switch virtual desktops independently on each monitor. After being able to do this, I don't understand why every window manager doesn't offer this. It's not uncommon with tiling WMs that have good multi-monitor support, but you really can't find it in traditional WMs. There's an unmaintained patch of openbox--openbox-multihead--that added the feature, and there's an "experimental" hybrid window manager written in Go (by the same author of the openbox patch), but no mainstream window managers appear to have the feature. Apparently it goes against a requirement/assumption in the EWMH spec and breaks existing pagers. But that's okay, because I don't use a pager.
Anyway, it really is critical to how I work now. I can keep a set of windows on my right monitor, and flip between virtual desktops on my center monitor without the right monitor changing at all. (And no, using the "sticky" feature of other WMs doesn't work for me because sometimes I do want to flip to a different virtual desktop on the right monitor and have that set of windows for whatever context I'm switching to). Along the same lines, the pertag patch is part of making dwm the perfect windows manager for me.
(If you're interested in the particular set of patches I use and my config, I maintain it at https://github.com/racingmars/dwm)
I use both i3 (actually Sway) and MacOS on a daily basis and they both support this feature. I agree I could not live without it.
I have never used dwm seriously, but as far as I can tell the main feature it offers over i3 is tagging. I don't really understand how this meaningfully changes the day to day workflow, and I'd love to hear what you consider to be the advantages.
Personally I prefer being able to quickly toggle a dynamic window layout based on my current workflow, and switch back to manual tiling when I specifically need to manually tile.
Currently I use Sway too as it's the most mature tiling compositor on Wayland, but once River WM[0], also based on wlroots, matures more I think I will likely make the switch because I often miss dynamic tiling.
[0] https://github.com/riverwm/river
On a side note, I hate how window moving works in Sway/i3. I can hardly ever get windows to move to where I want them to go with keyboard. As a result, I have a bind that enters a 'move' mode that takes the current selected window and moves it to a window that I can select. That, or I just use the mouse to drag the window, which is kinda annoying considering this is a keeb focussed environment.