Practical use of sysctl

I got a general question about sysctl. I understand how I can view and change kernel parameters but I'm struggling to think of parameters I might want to tweak. The video in chapter 25 shows how to change kernel.pid_max but that doesn't seem particularly useful (on my Fedora PC it's set to 4194304, which seems more than enough).

I looked into kernel.ctrl-alt-del and kernel.hostname. On my system kernel.ctl-alt-del is set to 0, which means the Ctrl-Alt-Del behaviour is managed by the init system. Changing the value to 1 didn't change its behaviour.

Next, I permanently changed my system's hostname by adding a file under /etc/sysctl.d/. This worked, and I was very proud of myself. However, when I cat /etc/hostname I am still seeing the old hostname. That makes me wonder why I would want change the hostname via sysctl. Simply updating /etc/hostname seems the right way to do this.

In short, I'm looking for some practical examples. Do any of you use sysctl to tweak settings?