Allow me to present you with a few scenarios, all of which recently happened.
A friend intended to boot his Windows partition, in order to update a laptop BIOS. By mistake he picked the “recovery” partition, easily done when GRUB’s OS prober can’t tell them apart. Without warning, it erases his GNU/Linux partition, leaving him stranded without a functioning bootloader (it couldn’t be bothered to install a functioning MBR while overwriting that sector). Luckily, he has a bootable USB memory, but all the data he cares about is in the lost partition.
Another friend is presented with a freshly erased memory card off a camera, from which photos need to be recovered.
I wanted to extract the music from a Playstation Portable game I own.
This is exactly what the two tools TestDisk and PhotoRec help with. The first finds lost file systems, and the second finds lost files. Both are incredibly easy to use and should be in your disaster recovery arsenal. They work, in many situations (don’t be fooled by “Photo” in the name), and are quite free. This is why I cared not one iota when my Lexar memory card didn’t come with the promised Image Rescue software.