"I am talking about trading, e.g. day-trading, short-term trading,'
What about dividends going to customer accounts, what about bonus issues of shares,. All positive. Defered settlement shares , while undergoing reconstruction you sell shares but no cash until later maybe a week or two.
Some people pay straight the way cash, other will take 3 days to pay, their broker will not pay for them remember T3 setllement.
Often when I buy parcel some is settled instantly and the rest is delayed. Go and see your maths teacher and ask for your money back. And give me a break.