I did Ipswich for a year or two
Zaitsev's got it right, mostly it's bringing stats into line with what's happening in the real world right now, particularly with regards to youth prospects who may or may not be showing the predicted talent that their Current/Peak Ability shows in the database.
Then there's other things like keeping in touch with comings and goings at the club, for instance ensuring that if one of your players is transferred out, the researcher in charge of his new team is made aware of him and his abilities.
Was very enjoyable, but time constraints stopped me from doing it in the last couple of years, mainly because I'm at a point where I'm trying to do lots of work for cash, so I'm having to let some of the freebies slide