When I landed to my new job I was surprised that nobody cleans up the portafilter, leaving this dubious privilege to whomever is lucky enough to fix them coffee next. My new coworker, a good guy and a coffee connoisseur explained me that there's a good reason for this. I've accepted that explanation but, quite honestly, completely forgot through the course of time. It's just became to me a fact, it's just the way we are doing it here.
So, years passed by, this question has been reasonably raised again, the good guy actually relocated and I've realised that I just don't have any reasonable answer other than "it's a tradition!".
So my question is - what is considered the best practice - to clean the portafilter immediately after making coffee or leave it till next round?