Difference between 'expiration date' and 'Password expiration date'?

[Turbo Fredriksson]

I was looking deeper into kadmin, and saw that there is an
'Expiration date: [never]' and 'Password expiration date: [none]'
in every principal... What's the difference?

If I dare a guess, the first expires the whole principal (including
password) and the last only expires the password... ?

If I'm right, why would I want to expire the whole principal!?