trading costs - commissions and bid-ask spread.
If you take 30 trades a week, you are paying a spread of 0.25 each time. Equals 7.25 ES points - you are losing this.
If you are taking 5 trades a week, you are losing 1.25 ES points in spread.
When i say 10 point stop, I am not referring to day trading only. I am advocating overnight holds, the most important point I am saying is trade in the direction of trend especially for first 6-9 months of your trading career. Easier than counter-trend trading.
Finally, 10 point stop and 20 point target - forces you to think and analyze. You can have a full day to analyze ES and then decide whether we are more likely to go to 1935 or 1895 and take a trade and stick to it. If you don't know, then don't trade. Maybe next week you will have a better idea of the way market is going, then trade.
If you ask me, Ideally you shouldn't take more than 3 trades in a week, when you are starting to trade. Just my experience and my 98 cents