The .ssh/config file allows to configure ssh aliases in quite an elegant way. Makes obsolete the need to remember full ssh server address, port, user or possibly different authentication file you'd need to pass.
.ssh/config file has lots of options, but for me, for now the most important are
Meaning, that if I run
ssh some_server in reality i'll issue
ssh -i ~/.ssh/some.key firstname.lastname@example.org -i.