Raw devices are a red herring, not related to the OP question about "possible disadvantages or limitations if you don't use a partition". A whole-disk file system could be accessed via the raw device or the block device, same as a partition.

Thanks for your intervention. I also don't see any context between raw access onto devices and my initial question. For now I can't see any weightly reasons that make the writing of a filesystem directly onto a dvice inadvisable, if the circumstances are given

What is the benefit though? Is it worth the lack of clarity that comes with departing from convention?

Conventions are important, true. The last sentence was rather related to the technical possibility.

Given that this has meandered, I am a little unclear as to what you are (now/still) asking.

There is no disdavantage in defining the full device (sans partition) as a filesystem. LVM users do it regularly.
Now, were you to invest in gpt disk, the discussion terminates.

Asking? Did I formulate any further question since my inital post?

Sorry - maybe I meandered between threads ...

Usable space... well, the only wasted space in a partitioned drive is the partition table, nothing else. And that's 512 bytes for MBR. Not a bid deal really.

About swap: not even having a swap file is any slower these days, because nowadays the kernel bypasses all the fs magic when accessing swap. So, it really doesn't matter if the swap lives in a dedicated partition, a raw disk or a file. The kernel will read the on-disk position directly, it's irrelevant. Well, you might wasted an extra microsecond while initializing the swap, that's about it...

Linux has no problem accessing these devices. The only problems can come from individual applications. Mostly low level tools, since the rest of the OS just deals with files and doesn't care about devices.

For example: your boot manager, testdisk, partitioning tools and that kind of stuff. However, any bootloader that can boot from a floppy or a cdrom (which are unpartitioned) shouldn't have any problem booting from sda instead of let's say sda1.

No, there's no advantage. There shouldn't (note the use of conditional) be any problem either.