Files can become damaged or put in disorder for a number of reasons including the main ones like: power failure, or any interruption to the system that occurs without the proper unmounting of filesystems; and, hardware faults, like problems with the moving parts or controller in rotating disks, or problems with the controller on solid state drives.
The fsck command can fix inconsistencies in the filesystem metadata and so restore the user's access to files. For example, fsck can restore or correct the data on the locations of files, and identify the locations of bad blocks if there are any on the drives it's working on. The fsck command can't fix the bad blocks because they are hardware flaws but those bad blocks can be marked in the metadata as unusable for the system. That will reduce the usable size of the drive by at least the size of the bad blocks, however large or small.
I'm not sure what this means:
I had cause to run this INITRAMFS the other day as the system had slowed then locked up
If the system booted with grub and stopped at a prompt that showed "initramfs", then the boot has stopped at the stage where the initramfs is creating the initial linux filesystem as part of the booting process before it finds the main root filesystem. There could be a number of problems, including problems with the filesystem that fsck can repair. There's usually a suggestion on screen when this happens which tells the user to run some command or to see a log file.
In any case, it looks like the fsck has corrected the system in your case, so there's no need to really do anything else since it boots properly after the fsck.
If you want to configure the initramfs, that can be done in the file: /etc/initramfs-tools/initramfs.conf, but there's no evident need to do that from the description of the issue.
