Or the Gentoo-one or Debian or even the Kernel docs regarding resume=<partition>. There are a few things to consider:
- it does not work on encrypted partitions since there is no way to unwrap any key at all
- with an active state originating from an encrypted partition gives any attacker the opportunity to manipulate the hibnerated system image
- hardening tools often recommend to turn off hibernation in the kernel completely because of #2 (and the implication that this would load any crafted image into your working memory)
- recent distributions create /tmp as a tmpfs/ RAM disk which makes hibernation impossible due to power loss of RAM in this sleep state, and /tmp could be the default if nothing else is specified
- partition parameters on kernel command lines rise and fall with modules available at boot time/ through the bootloader, e.g. GRUB or Lilo. It might happen that using UUID in the case of hibernation does not work in combination with certain bootloader versions
- hardware does not support the power down sleep state, e.g. Raspberry PI or has no peripherals connected triggering a boot process (BIOS does this upon pressing for example the shutdown-key on a USB-keyboard with this enabled in the BIOS which in turn requires the USB-ports to be monitored/ enumerated and powered which isn't the case for any Raspberry)
I've been using hibernation for more than a decade on different hardware and distributions but only on that drag-around low-fi laptop ingesting ycombinator, running IRC client or Liferea. I always use the swap partition for this and it has always been /dev/sda2 with 4GByte (currently 5.4.* for Arch, Gentoo and Debian). I trust Grub, currently 2.x but also worked back in the days with 1.x since it is a kernel parameter (and the kernel self-compiled with CONFIG_HIBERNATION=y and copied with a steady hand and a magnetized needle).