The quoted text said “TrueNAS software”, which is true, it was not designed to use combined boot & data volumes. When iX took over FreeNAS, they continued development using separate boot device & data device(s).
I am not trying to stop anyone from doing anything they want. My intent was to help people understand that building a minimal computer to use as a server might have odd performance or failure conditions not generally experienced by others using server grade hardware.
As an example, while ECC RAM is not required by ZFS or TrueNAS, we have seen some odd failures where a ZFS pool can't be imported due to severe corruption. Some pool corruption problems were tracked back to other causes.
However, a few never had a good explanation. My “guess”, (and it really is just a guess), is that some of those unexplained pool corruption cases were caused by memory faults or bit flips. Rare, but you don’t want to be the one that has such.
Another example is that people persist in considering power failures as ways ZFS pools get corrupt. This is not true, and I wrote about why that is not the case:
Of course, if the power failure causes a hardware failure, like damaging a disk, well, of course that could lead to pool corruption.
So, my intend is to pass information that might help a person make a reliable NAS and avoid data loss. But, they are free to ignore me, or discuss details