They're fanless and low-power, which was the primary draw to going this route. I run a Kubernetes cluster on them, including a few personal websites (Nginx+Python+Django), PostgreSQL, Sonarr, Calibre, SSH (occasionally) and every once in a while, an OpenArena server :-)
I did a 4 node Pi4 kubernetes cluster for about 5 years. The learning experience was priceless. I think most notable was learning to do proper multiarch container builds to support arm and x86_64. That being said, about half a year ago I decided to try condensing it all into two n100 nuc-like clones and keep one pi as the controller. For me and my apps and use cases there was no going back. Performance gains were substantial and in this regard I think I was hobbling myself after the educational aspect plateaued.
Actually, as a web guy, I find the ARM architecture to be more than sufficient. Most of the stuff I build is memory heavy and CPU light, so the Pi is great for this stuff.