The merits of a partitionless filesystem
So I've got a block device, say
/dev/loop0. Clearly if I want to boot from the former, or I want to subdivide it into segments with separate filesystems, I need to partition it. But suppose I don't have those needs. Instead, I just plan to use my entire block device as storage. Maybe I'll make it part of a raid volume, or maybe I'll encrypt it with cryptsetup, or maybe I'll make it a PV for LVM. Or maybe I just want to install a filesystem on it directly. In at least some of these cases, there doesn't seem to be any technical obstacle to using the device unpartitioned. That's what we generally do with block devices generated by losetup, and one can do it too with regular hard disks. I know because I've done it.
Now, there are dangers to this. For instance, if you ever go on to run
fdisk /dev/sda, you won't see anything sensible. And you might accidentally write a partition table or something like that to your device, and then the data you had on the unpartitioned device would be hosed. Maybe if you even boot into Windows with the device attached, it will get hosed. People tell scary stories.
But I'd just like to understand, if the device is only ever connected to your Unix setup (and to keep things simple, let's stick to Linux only), and you never try to write a partition table or MBR to it or anything like that, are there any other downsides to using a storage device unpartitioned? I'm not proposing to do it; I just want to understand what the genuine reasons for not doing it are.
On the flip side, is there any obstacle or downside to partitioning the block device
/dev/loop0? Perhaps there'd be no advantage to doing so. But I expect it would work, wouldn't it? Here, too, I'm only asking because I want to understand the reasons behind our standard practices.