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Providing cash up front allows you to use that to leverage your position on a particular stock. This will accelerate your holdings, accelerate the amount of dividends and accelerate the capital position when the particular stock appreciates in price.

The downside is, if heavily leveraged (up to 70% on most accounts) and the stock declines then huge losses will occur and thus wreak havoc on a portfolio, of which the investors portfolio will never recover. Allowing for this not to occur, incorporate a 'margin of safety' when dealing with leverage.