What happens when we uncomment GRUB_DISABLE_LINUX_UUID=true?

• Well i think the comment above that line says it all
  # Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux

• After uncommenting that line root= will be passed as device name and not UUID.

  linux /boot/vmlinuz-2.6.30-1-amd64 root=UUID=...
  to
  linux /boot/vmlinuz-2.6.30-1-amd64 root=/dev/sdX

• However it is not recommended to uncomment that line,coz if you delete/create a new partition the partition table will get changed.
• So that you cant boot into the system.

when uncomment it, the next time grub regenerates /boot/grub.cfg will put absolute device names instead of UUID- i.e. /dev/sdXY

so if you re-arrange partitions in partition table (for example insert/delete partitions) and partition numbers changed- grub can't find the kernel to boot

with UUID, even re-arranging the partitions won't break things

the con of UUID is that its hard to they are long and therefore hard to remember.