.... I’m not keen, prefer to know exactly what’s mine rather than guess work, particularly in a large group.
However I’ve recently been out with DH and have been 
by his sharing board etiquette.
The first one was bread/cheese/meat on a board and DH put exactly half of the whole board into each of our plates ... at once! Shouldn’t you just pick at it, isn’t that the point?
Second meal out the other Sunday and it was a new place that served a lovely roast on a wooden board - for two people if you ordered the same. He did it again .... took exactly half if everything and piled his plate up, I stopped him doing the same with mine.
Should have taken him to the bloody local Toby carvery!