It’s a much more intimate experience and we formed relationships with people without even being able to speak at a conversational level.
This means that every time you want to sip your drink you have to entertain this needless protocol: identify someone around the table - preferably someone you have yet to drink with - say cheers (translation required), and sometimes drink all of the 60 mL cup at once. You should also keep a checklist of who you have and haven't drunk with. The more political, the greater the need to move around the table at random intervals, shake hands, and drink. This is a demonstration often devoid of meaning.
If it's a real party it can be fun to bottoms-up all the drinks. For a more relaxed meal & conversation setting (my preference), as an outsider this is uncomfortable. It ruins the slow enjoyment of expensive alcohol. Why can't I sip my own damn drink with my meal?!
Also as someone who drinks a lot less as I get older, I lately find myself not drinking at all at these events, because there is no middle ground.
It was totally acceptable to sip a drink. If I was empty and needed a refill I would simply take the shared container (650ml beer bottle, tea pot, etc.) and first refill someone or everyone’s drink, empty or not. Essentially the personal containers were bottomless.
I never felt an obligation to refill a specific person’s drink. But that situation never really came up because everyone eventually is the person initiating the refills.
It’s possible I was offending a lot of people. In fact it is likely. They were certainly generous enough to not say so however.