Say you work for an organisation with multiple servers divided in clusters. There are clusters where you use the same credential to log in to some or each server within the cluster. If I create a login entry for each server, I need to repeat the credential. Now if the company policy requires me change the password for every couple of months, this means that need to remember to retype the password into all relevant entries. It would be handier if there were just one place to change the password and this change would be automatically reflected in the correct login entries.
I know that you can create a secure note with Notes containing your credential and Custom field to every server, but I find it a little clumsier way to organise this.