“Cleanliness is next to godliness” say (supposedly) ancient Hebrew writings.
Highly applicable to making good espresso.
When you’ve just blasted (almost) boiling water at high pressure through finely ground coffee beans to extract the flavour and the oils that emulsify to create a crema, why wouldn’t you clean your equipment?
Nothing contributes to a scroungy espresso like rancid oil and reused coffee grounds…
(Needless to say at Paul Bonna’s ever-excellent kaffeekommunezwei)