While you are right that it would be better to never need tweaking the number of buffers, all your links show such a problem caused by the same application, the firewall pf.

I assume that for some reason pf consumes more buffers than other applications, so it is likely to cause such problems. So pf users should preemptively change the default configuration.

I have never used pf, because I prefer the native FreeBSD firewall, both to pf and to the Linux firewall.

With the native firewall and with the many other networking applications that I have run, I have never seen buffer exhaustion, and like I have said, the mean time between reboots was well above a year.

FreeBSD and the other *BSDs have always been famous for not needing reboots, even after years of continuous operation. For this goal, avoiding memory fragmentation caused by dynamic allocation is essential. Thus static allocation for various kinds of resources might be necessary.