If you decide to put everything in one large partition (not really recommended), always make sure /usr/local is on its own partition. If you do not do that, some ports will core dump. If you use one big partition, you will need to disable an important security feature to allow the ports to run.
They assume since it's your disk you best know how to partition it. One is free to edit the default save them to file for next time.
If one wants to manage the details of a computer system with documentation describing the implications of each decision OpenBSD is perfect.
There are plenty of other operating systems that will most do the right thing. How many operating systems do exactly what you tell it to?
Then it shall have some documentation on system requirements.
I tried to install Freebsd on a VM with UFS as a filesystem and the show ended with out of inodes when installing the ports system. This in 2020 is a bit sad.
What ports are you talking about? I'm using FreeBSD as my daily driver, never had a port core-dump due to this.
OpenBSD prohibits this except when code is run from a partition that permits it by means of a mount flag. Otherwise you get a core dump.
And all the partitions are largely an availability feature: if errant code fills up /var/log then /home is still usable.
I'm aware of that if no partitions are filled it causes an domino effect if not on its own partition. I have ZFS quotas configured so surely that mitigates the issue?
Handy to know though.
"On platform X, you must do A."
"Huh, weird, that's never affected me using (thing that only runs on platform B)."