It is difficult to consistently make money with only one contract at a time: every decision you take will be a six or nix. Because you can not afford to lose, you will either get stopped out to soon or take profits too soon, never making good money.
It is frustrating to see the market running further in your trade direction moments after you took profit, or were stopped out of a trade.
Very often the result will be a revenge trade where you emotionally and impulsively jump back into the market (without a plan) just to be whiplashed and losing all the profits you made.
Trading more than one contract will always leave you with a chance to catch a home run with part of your position on a trade.
The use of a well-planned and executed Stop Loss strategy is one of the most important tools you have to survive as a trader.
There are various ways to calculate Stop Loss levels. It will depend on the kind of risk you are willing to take.
I use two types of Stop Loss strategies, the initial Stop Loss (Trading Stop Loss) that is put in place when you execute the trade, and a trailing (progressive) Stop Loss that follows the price.