When I installed Kubuntu on my wife's new laptop I entered her name for the initial user account. That results in uid and gid 1000 given to her user. On my desktop, my user has uid and gid 1000, her user has 1001 for both. When exchanging files, even more when setting up an NFS server later, all users on the network should have the same uid and gid on all computers.
That's when I googled and came up with an excellent description for usermod and groupmod that help in that situation.
In addition, I found the -h parameter of chgrp and chown useful, so symbolic links get corrected too, not only the referenced files.